oou^i^iiSE 


'  HEALTH 


Columbia  WLnibtx&ilp 
in  tfje  Cttp  of  J^eto  fiorfe 

College  of  iPftpstcians;  anb  ismrgeons; 


Reference  llibvavp 


Presented  by 

&  DR.  WILLIAM  J.  GIES  Jf 

to  enrich  the  library  resources 

available  to  holders 

of  the 

GIES  FELLOWSHIP 

in  Biological  Chemistry 


Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 

Open  Knowledge  Commons 


http://www.archive.org/details/dentalelectrotheOOstur 


DENTAL 
ELECTRO-THERAPEUTICS 


BY 

ERNEST  STURRIDGE,  L.D.S.  Eng.,  D.D.S. 

FELLOW    OF    THE    ROYAL    SOCIETY    OF    MEDICINE,    MEMBER    OF    THE    BRITISH     DENTAL     ASSO- 
CIATION,   MEMBER    OF     THE    BRITISH     SOCIETY     FOR     THE     STUDY    OF    ORTHODONTICS, 
ASSOCIATE  MEMBER  OF  THE  AMERICAN  DENTAL  SOCIETY  OF  EUROPE,  MEMBER 
OF    THE     AMERICAN     DENTAL     SOCIETY     OF     LONDON,     CONTRIBUTOR 
ON     DENTAL    ELECTRO-THERAPEUTICS    IN    "THE    SCIENCE    AND 
PRACTICE  OF  DENTAL  SURGERY,"  ETC. 


ILLUSTRATED  WITH   154  ENGRAVINGS 


LEA  &   FEBIGER 

PHILADELPHIA    AND    NEW    YORK 
1914 


Entered  according  to  the  Act  of  Congress,  in  the  year  1914,  by 

LEA   &   FEBIGER, 
in  the  Office  of  the  Librarian  of  Congress.     All  rights  reserved. 


PREFACE 


The  urgent  necessity  for  literature  on  dental  electrothera- 
peutics, and  especially  on  the  technique  of  this  branch  of  sci- 
ence, has  been  brought  to  the  author's  notice  bjT  the  number 
of  requests  he  has  had  from  time  to  time  from  fellow  prac- 
titioners for  information  on  electrical  treatment  of  dental 
diseases.  In  the  majority  of  inquiries  lack  of  knowledge 
of  electro-physics  has  been  frankly  admitted,  so  that  informa- 
tion on  technique,  in  the  author's  opinion,  would  ultimately 
lead  to  failure  in  the  use  of  the  current  for  dental  treat- 
ment. He  is  convinced  that  in  order  to  carry  out  electrical 
treatment  successfully  it  is  necessary  to  study  electro- 
physics  so  far  as  it  pertains  to  electro-medicine,  and  also 
the  physiological  and  therapeutic  effects.  For  the  pur- 
pose of  bringing  this  important  subject  to  the  notice  of 
the  profession  he  has  undertaken  in  this  work  to  produce 
a  concise  and  condensed  treatise  on  the  fundamental  prin- 
ciples of  dental  electro-therapeutics;  he  has  endeavored 
to  be  explicit  on  essential  principles,  and  if  he  is  able  to 
lay  any  claim  to  originality  in  details  of  technique,  he  fully 
acknowledges  the  assistance  he  has  obtained  from  the 
medical  branch  of  the  science.  Tin's  work  is  especially 
intended  to  bring  forward  the  value  of  ionic  medication  in 
the  treatment  of  periodontal  disease,  and  everything  per- 
taining to  ions  and  their  use  in  dental  treatment  has  been 
carefully  detailed,  with  the   hope  of   exciting  the  interest 


IV  PREFACE 

which  the  subject  warrants.  It  is  only  necessary  fully 
to  understand  the  efficacy  of  this  method  of  treatment 
to  appreciate  the  value  of  ionic  medication  to  the  dental 
profession  in  these  days  when  the  medical  profession  looks 
first  to  the  dentist  to  deal  with  oral  sepsis  to  which 
is  attributed  alimentary  toxemia  with  its  many  serious 
consequences. 

Treatment  by  ionic  medication  is  within  the  reach  of 
every  dentist,  but  a  word  of  warning  is  necessary  to  those 
who  are  attracted  by  its  reputed  usefulness:  do  not  ap- 
proach the  subject  lightly,  study  carefully  sufficient  electro- 
physics  to  understand  the  nature  of  the  current  with  which 
you  are  dealing,  and  obtain  a  knowledge  of  the  electro- 
physiological effects,  and  then  the  therapeutic  effect  will 
be  most  gratifying. 

The  author  has  endeavored  to  explain  the  principles  of 
ionic  medication,  and  has  included  considerable  technique, 
with  the  intention  that  this  method  may  in  no  way  be 
confounded  with  the  phenomenon  of  cataphoresis,  which, 
he  has  pointed  out,  is  not  the  effect  obtained  in  using  the 
current  on  oral  tissues. 

The  subject  of  high  frequency  currents  has  been  simply 
touched  upon,  but  it  is  an  important  branch  of  electro- 
therapy, and  one  which  is  gaining  ground  rapidly  in  dental 
treatment.  Those  interested  in  this  branch  are  referred 
to  larger  works  of  medical  writers  for  further  information. 

The  author  acknowledges  with  much  gratitude  the  assist- 
ance given  by  his  friend  Dr.  C.  H.  Abbot,  of  Berlin,  in  writing 
the  chapter  on  away  technique  and  diagnosis,  and  he  also 
thanks  Mr.  Charles  Clark,  of  London,  for  his  contribution 
on  the  apparatus.  He  is  indebted  to  Dr.  N.  S.  Finzi,  of 
London,  to  whom  he  wishes  to  express  his  sincere  thanks  for 


PREFACE  v 

valuable  assistance  in  correcting  and  revising  manuscripts, 
and  for  many  useful  suggestions  in  connection  with  this 
work.  He  courteously  acknowledges  the  free  use  of  those 
medical  authors'  books  from  which  he  has  obtained  much 
useful  information,  especially  Dr.  Lewis  Jones,  of  London, 
Professor  Leduc,  of  Nantes,  and  Dr.  Tousey,  of  New  York. 
His  best  thanks  are  due  to  Mr.  B.  Jones  for  information 
on  the  mechanism  of  dental  electrical  appliances,  and  to 
Messrs.  C.  Ash  &  Sons,  Ltd.,  Messrs.  K.  Schall  &  Son, 
the  Cavendish  Electrical  Co.,  Ltd.,  and  others  for  the  loan 
of  blocks. 

E.  S. 


CONTENTS 


PART  I. 
ELECTRO-PHYSICS. 

CHAPTER   I. 

Frictional  or  Static  Electricity. 

Theories  as  to  the  Nature  of  Electricity — Electroscope — Leyden  Jar 

— Conduction — Induction — Statical  Machines 17-27 

CHAPTER  II. 

Galvanic  Electricity. 

Volta's  Contact  Law — Electrolytes — Voltic  Cells — Electro-Motive- 
Force — Practical  Electrical  Units — Resistance — Heat  Effect  of 
the  Current — Polarization — Poles — Testing  the  Poles — Electro- 
lysis— Ions — Electro-positive,  Electro-negative        ....        28-53 

CHAPTER  III. 

Cells. 

Leclanche  Dry  Cell — Smee  Cell — Bichromate  of  Potash  Cell — Persul- 
phate of  Mercury  Cell — Bunsen  Cell — Grove  Cell — Daniell  Cell — 
Secondary  Batteries  or  Accumulators — Edison  Storage  Battery- 
Arrangement  of  Cells — Cells  in  Series — Cells  in  Parallel — Cells 
in  Multiple  Arc — Density 54-74 

CHAPTER  IV. 

Magnectic  Field — Dynamo  Currents — Batteries. 

Induced  Currents — Self-induction — Induction  Coil — Secondary  Coil — 
Continuous  Current — Alternating  Current — Transformers — Bat- 
teries—  Home-made  Battery — Switchboards  for  Voltic  Cell 
Battery — Cautery  Battery — Accumulator  Battery — Induction 
Coil  Battery 75-108 


vni  CONTENTS 

CHAPTER  V. 

Battery  Accessories. 

Current  Collectors — Milliampere  Meter — Rheostats — Commutator — 
Rheophores — Electrodes — Rheostat  for  Direct  Current  from 
Main — Resistance  for  Heavy  Currents — Alternating  Current 
Transformers — High  Frequency  Currents 109-139 

CHAPTER  VI. 

Dental  Electrical  Apparatuses  and  Appliances. 

Motors — Electric  Engines — Electric  Lathes — Switchboards — Accumu- 
lators— Direct  Resistance  Motor  Converter — Electric  Hot-air 
Syringe — Electric  Sterilizers  and  Hot  Water  Apparatus — Foot- 
warmer —  Electric  Furnaces  —  Pyrometer  —  Electric  Gold  An- 
nealer 140-155 

CHAPTER  VII. 
The  Rontgen  Rays. 

X-ray  Apparatus — Technique  of  Dental  Radiography — X-ray  Diag- 
nosis  156-210 


PART  II. 
ELECTRO-THERAPEUTICS. 

CHAPTER  VIII. 

Electro-physiological  Effects. 
General  Considerations — Conduction  by  Ions 211-219 

CHAPTER  IX. 
Physiological  Effects  of  Current. 

Cataphoric  Effect — Electrolytic  Effect — Path  of  the  Current  in  the 
Body — Motor,  Sensory,  and  Special  Nerve  Effects — Effect  of 
Current  on  Nutrition — Effect  of  Current  on  Salivary  Glands — 
Resistance  Effects  of  Current  Passing  through  the  Body     .    220-238 


CONTENTS  ix 

CHAPTER  X. 

Electro-therapeutic  Effects. 

Ionic  Medication — From  a  Dental  Aspect — The  Zinc  Ion — The 
Copper  Ion — The  Iodine  Ion — The  Silver  Ion — The  Cocaine  Ion 
— The  Adrenalin  Ion — The  Salicylic  Ion — Advantages  of  Ionic 
Medication — Effects  of  Ions  on  Bacteria 239-258 

CHAPTER  XI. 

Technique  of  Ionic  Medication  in  Dental  Operations   .   259-263 

CHAPTER  XII. 
High  Frequency  and  Static  Currents. 
X-ray  and  High  frequency  Currents 204-270 

CHAPTER  XIII. 

Electro-therapeutics  in  Dentistry. 

Treatment  of  Dead  Teeth — Periodontitis  from  Septic  Pulp — Acute 
Local  Periodontitis — Perforation  of  the  Apex — Perforation  of  the 
Side  of  the  Canal — Alveolar  Abscess — Chronic  Alveolar  Abscess 
— Necrosis  of  the  Jaws — Marginal  Gingivitis 271-279 

CHAPTER  XIV. 
Treatment  of  Pyorrhcea  Alveolaris. 

Pericdontal  Disease — Incipient  Infection  of  the  Gingival  Trough — 
Septic  Infection  of  Gingival  Trough  without  Suppuration — Septic 
Infection  of  Periodontal  Membrane — Acute  Septic  Infection  of 
Gums  and  Periodontal  Membrane — Chronic  Septic  Periodontitis 
(Pyorrhcea  Alveolaris) 280-297 

CHAPTER  XV. 

Anaesthesia — Bleaching — Neuralgia. 

Anaesthesia  of  Sensitive  Dentine  for  Immediate  Extirpation — Anaes- 
thesia of  Gums  and  Alveolus — Electrolytic  Tooth  Bleaching — 
Bleaching  with  Chlorinated  Lime  —  Bleaching  with  Hydrogen 
Dioxide— Neuralgia       .      .  298-312 


DENTAL  ELECTRO-THERAPEUTICS. 


PART  I. 
ELECTRO-PHYSICS. 


CHAPTER  I. 
FRICTIONAL  OR  STATIC  ELECTRICITY. 

Theories  as  to  the  Nature  of  Electricity — Electroscope — Leyden  Jar — 
Conduction — Induction — Statical  Machine. 

The  study  of  electrical  science  embraces  a  wide  and 
varied  field.  Many  of  the  phenomena  are  well  known  and 
are  placed  on  sure  and  scientific  footing.  Hypotheses  have 
been  suggested  by  eminent  modern  works  in  physics  which 
connect  electricity  with  "the  ether"  in  a  way  comparable 
with  light  and  heat. 

The  manifestations  of  electricity  with  which  we  have 
most  to  do  from  a  dental  aspect  are  those  of  energy,  force, 
and  power,  and  in  order  to  understand  how  these  are 
brought  about,  and  how  they  can  be  utilized,  the  study  of 
electricity  should  be  undertaken  from  the  very  primitive 
forms  of  electrical  phenomena  which  have  been  known  for 
ages,  to  the  very  latest  discoveries  of  the  effect  of  the  current 
from  a  therapeutic  standpoint. 

A  primitive  electrical  phenomenon  was  observed  by 
early  workers  in  the  science,  who  noted  that  when  certain 
substances  are  rubbed  together  a  current  of  electricity  is 
generated,  which  is  possessed  of  certain  definite  properties. 


IS  ELECTRO-PHYSICS 

The  character  of  the  current  and  the  effect  produced 
depend  on  the  method  of  exciting  it  and  the  substance 
used. 

From  these  early  experiments  in  the  production  of 
electric  current,  methods  have  gradually  developed  into 
the  present  day  elaborate  plans  for  the  production  of 
electricity. 

It  is  said  that  Greek  philosophers,  many  hundred  years 
b.  c,  noted  that  when  amber  was  rubbed  with  cloth  it  had 
the  power  of  attracting  other  bodies,  but  it  was  Dr.  Gilbert, 
of  Colchester,  an  Englishman,  who  in  the  later  part  of  the  six- 
teenth century,  made  a  study  of  this  phenomenon,  and  who 
by  experiments  determined  which  bodies  would  and  which 
would  not  acquire  the  property.  He  also  gave  the  name 
of  Electricity  to  the  cause  of  this  attraction.  He  tested 
substances  by  bringing  them  near  a  metal  needle,  lightly 
balanced  on  a  pivot. 

If  we  rub  a  glass  rod  with  silk,  or  a  piece  of  sealing  wax 
with  flannel,  the  friction  will  excite  electricity  in  the  rubbed 
end  of  glass  or  wax,  and  if  we  apply  them  to  some  light 
substance,  such  as  scraps  of  paper  or  a  suspended  pith 
ball,  we  shall  find  that  they  will  attract  these  bodies. 

If  we  suspend  a  ball  of  elder-pith  by  a  silk  thread  attached 
to  the  end  of  a  ruler,  and  apply  the  piece  of  silk,  which  has 
been  used  to  rub  the  glass  rod,  we  shall  find  that  the  pith 
ball  will  be  repelled.  It  is  clear  that  there  are  two  forces 
excited,  the  one  on  the  glass  rod  which  attracts,  and  the 
other  on  the  silk  which  repels  the  pith  ball.  The  sub- 
stances which  have  been  rubbed  have  always  contained 
electricity,  and  although  the  one  attracts  and  the  other 
repels  the  pith  ball,  it  is  not  that  there  are  two  kinds  of 
electricity,  but  only  two  degrees  of  the  same  current;  in 
other  words,  there  is  a  difference  of  power  or  potential. 
The  approach  of  the  glass  rod  to  the  pith  ball  alters  the 
balance  of  electricity  in  the  ball  by  inducing  a  current  on 
the  side  nearest  the  rod  of  opposite  sign  to  that  on  the  rod, 
the  further  side  is  charged  with  current  of  the  same  sign  as 
that  on  the  rod. 


FRICTIONAL  OR  STATIC  ELECTRICITY  19 

"Bodies  charged  with  unlike  electricities  attract  one 
another  and  bodies  charged  with  like  electricities  repel," 
or  in  the  light  of  recent  research,  the  current  from  the  body, 
which  is  more  highly  charged,  tends  to  flow  toward  that 
in  which  there  is  a  deficiency  of  charge,  or  away  from  that 
in  which  there  is  already  a  charge;  in  other  words,  there 
tends  to  be  a  leveling  up. 

The  term  positive  (  +  )  electricity  is  applied  to  current 
of  greater  power,  and  negative  ( — )  electricity  to  the 
lesser,  the  differences  are  only  potential,  quantity,  direction 
of  flow,  and  rate  of  variation  of  these. 

Metals  do  not  become  perceptibly  electrified  when 
rubbed  with  other  substances  in  the  same  way  as  glass  or 
sealing  wax,  because  they  possess  the  power  of  conducting 
electricity;  friction  fails  to  disturb  the  balance  of  electricity 
in  a  substance  which  so  conveys  electricity,  a  good  con- 
ductor, as  it  is  called,  because  any  disturbance  is  promptly 
neutralized  by  the  electricity  flowing  back  to  the  point 
from  which  it  was  displaced. 

Electricity  may  also  pass  from  one  substance  in  which 
it  has  been  excited  to  another  which  has  affinity  for  it, 
without  actually  being  brought  in  contact  with  it;  that  is, 
it  may  pass  through  an  intervening  air  space  and  charge 
another  body,  or  a  current  of  opposite  sign  may  be  excited 
in  a  body  brought  near  a  charged  body,  from  which  it  is 
insulated.  This  effect  is  brought  about  by  induction 
(see  p.  24). 

Theories  as  to  the  Nature  of  Electricity. — A  theory  was 
propounded  by  Robert  Symmer  in  1789  which  is  generally 
known  as  the  two-fluid  theory,  in  which  it  is  advocated 
that  every  body  contains  an  unlimited  store  of  electric 
fluid  of  two  opposite  kinds  which  neutralize  one  another, 
being  of  equal  amounts,  the  positive  and  negative  kinds. 
These  two  electric  fluids,  he  assumed,  are  capable  of  being 
divided,  when  they  are  excited  by  friction  or  otherwise, 
and  the  body  which  contained  the  greater  amount  of  fluid 
is  positively  electrified,  and  that  which  contains  the  lesser 
negatively    electrified.      This    hypothesis,   which,    whether 


20  ELECTRO-PHYSICS 

regarded  as  true  or  not,  possesses  an  analogous  bearing  on 
facts  which  frequently  must  be  referred  to. 

Another  theory  which  was  suggested  by  Sir  William 
Watson  in  1747,  and  further  elaborated  on  by  Benjamin 
Franklin,  is  that  there  is  but  one  kind  of  electricity,  that 
when  the  current  is  excited  or  set  in  motion  by  friction  or 
otherwise,  one  body  becomes  possessed  of  more  current 
than  the  other  at  the  expense  of  the  other,  the  former  being 
positively  and  the  latter  negatively  electrified.  This  theory 
is  often  referred  to  as  the  one-fluid  theory.  Other  views  on 
electricity  may  be  obtained  from  such  authors  as  Green, 
Stokes,  Maxwell,  and  Oliver  Lodge. 

The  latest  theory  is  that  propounded  by  Prof.  J.  J. 
Thomson,  of  Cambridge,  at  the  beginning  of  the  present 
century.  "According  to  this,  electricity  is  regarded  not 
as  a  fluid,  but  yet  as  having  real  existence  in  the  form  of 
minute  fragments  called  Electrons.  Definite  information 
has  been  obtained  as  to  the  size,  etc.,  of  only  one  kind  of 
electron,  that  which  conveys  negative  electricity.  It  is 
possible  that  positive  electrons  also  exist.  These  negative 
electrons  can  exist  alone :  when  in  motion  they  form  an  elec- 
tric current.  They  can  become  attached  to  the  atoms  of  a 
solid  body,  and  the  body  is  then  negatively  charged.  Each 
atom  of  an  ordinary  solid  body  is  supposed  to  contain 
many  such  negative  electrons,  paired  off  with  an  equal 
number  of  positive  electrons,  and  if  any  of  these  negative 
electrons  are  torn  away  the  body  is  left  positively  charged. 

"The  process  by  which  a  metal  conducts  electricity 
probably  consists  in  the  passing  of  electrons  from  one 
immovable  molecule  in  the  solid  body  to  the  molecule  next 
to  it.  The  mass  of  each  of  these  electrons  is  the  same,  and 
only  about  fwu'  °^  that  of  the  lightest  atom  known  (that 
of  hydrogen)."  This  concise  explanation  of  the  electron 
theory  is  taken  from  C.  E.  Ashford's  Electricity  and 
Magnetism. 

The  Electroscope. — We  have  noted  that  electricity  of 
unlike  kinds  generated  by  friction  attracts,  and  that  like 
repels  each  other.    To  tell  when  a  body  is  electrified,  and 


ELECTROSCOPE 


21 


which  kind  of  electricity  it  is   charged   with,  the  electro- 
scope is  an  easy  means. 

There  are  many  forms  and  modifications  of  the  electro- 
scope.    One  of  the  simplest  is   the  gold-leaf  electroscope. 
This  consists  of  a  vessel  in  which  is  suspended  by  a  metal 
wire  two  strips  of  gold-leaf  placed  slightly 
apart.     The  wire  is  connected  to  a  brass  FlG-  1 

rod,  which  passes  through  the  centre  of  the 
cork  in  the  jar  and  terminates  in  a  metal 
plate  or  knob.  If  we  approach  the  knob 
of  the  electroscope  with  a  glass  rod,  which 
has  been  charged  with  positive  electricity 
th,e  charge  will  pass  to  the  gold-leaf,  both 
strips  become  positively  charged  and  repel 
each  other.  Similarly,  if  a  negatively 
charged  substance  be  applied  to  he  un- 
charged electroscope,  the  gold  leaf  will  be 
repelled.  If  the  electroscope  be  affected 
by  a  charged  body  whose  sign  we  desire 
to  determine  by  bringing  in  contact  an  Electroscope. 
electrified  glass  rod,  if  it  be  positively 
charged  the  gold-leaf  will  diverge  still  further,  but  if 
negatively  charged  the  gold-leaf  will  collapse.  The  glass 
rod  used  to  test  the  electroscope  will  lose  none  of  its 
electrification,  and  on  removing  it  the  gold-leaf  will  relapse 
into  its  former  position. 

This  sensitive  instrument  will  determine  if  a  body  is  only 
slightly  charged  with  electricity;  if  the  gold-leaf  diverge 
ever  so  little  the  body  is  charged. 

The  Leyden  Jar. — This  is  a  convenient  form  of  condenser 
and  collector  of  electricity.  It  is  usually  constructed  of  a 
glass  jar  lined  with  tin-foil  on  the  inside  to  within  a  few 
inches  of  the  top,  and  similarly  coated  on  the  outside. 
Through  the  cork  is  passed  a  brass  rod  which  terminates 
externally  in  a  knob,  and  after  going  more  than  half-way 
into  the  jar,  terminates  in  a  brass  chain  resting  on  the 
metallic  lining  of  the  bottom  of  the  jar.  The  foil  lining 
the  inside   and   coating   the   outside   constitutes   the   two 


22 


ELECTRO-PHYSICS 


Fig.  2 


Leyden  jar. 


conductors,    the   glass    intervening,    the    dielectric    of   the 
condenser. 

To  charge  the  jar  the  knob  is  connected  with  the  con- 
ductor of  a  working  frictional  machine,  and  the  outer 
coat  is  connected  with  earth,  the  charge  passing  to  the 
inner  coating  of  the  jar  acts  on  the  outer 
coating  through  the  intervening  dielectric  by 
induction.  This  induced  current  is  conveyed 
away  to  earth,  leaving  a  charge  of  opposite 
sign  held  there  by  the  charge  on  the  inner 
coat.  This  increases  the  "capacity"  of  the 
inner  coat. 

To  discharge  the  jar  it  is  only  necessary 
to  bring  a  conductor  which  is  in  contact 
with  the  outer  coat  near  to  the  knob  of  the 
jar,  when  a  spark  will  occur  by  the  coming 
together  of  the  two  electricities,  thus  estab- 
lishing equilibrium. 

The  quantity  of  electricity  which  the  con- 
denser will  contain  depends  on  the  surface 
area  of  the  metallic  lining  and  the  strength  of  the  dielectric. 
If  the  Leyden  jar  is  made  of  very  thin  glass,  and  a  charge 
of  very  high  potential  passed  into  it,  it  is  liable  to  be  broken 
by  the  strain  and  a  spark  passes. 

The  phenomenon  of  the  discharge  of  the  Leyden  jar, 
which  takes  place  with  sudden  oscillations  and  a  spark, 
enters  into  the  principle  of  the  construction  of  many  ap- 
paratuses made  for  electrical  treatment.  The  capacity  of 
the  jar  varies  with  the  area  of  the  conducting  surfaces  and 
the  thickness  of  the  dielectric.  If  the  area  is  large  and  the 
dielectric  thin,  the  capacity  will  be  greater  than  if  the 
dielectric  is  thick  with  the  same  area — that  is,  the  capacity 
of  the  jar  is  greatly  increased  if  the  area  is  increased  and 
the  dielectric  remains  the  same  thickness. 

Conduction. — The  conduction  of  electricity  up  to  a  point 
resembles  that  of  heat,  especially  when  we  think  of  it  as 
being  conveyed  along  a  metal.  In  whatever  way  an  electric 
current   moves   it   certainly   is   transferred   from   point  to 


CONDUCTOR  23 

point  by  a  certain  class  of  substances,  which  when  they 
permit  of  the  free  passing  of  electricity  are  known  to  us  as 
conductors,  while  other  substances,  which  only  allow  of 
very  little  passing  or  apparently  no  passing  of  current  we 
call  non-conductors.  If  the  gold-leaf  of  the  electroscope 
be  suspended  by  glass  or  vulcanite  or  some  such  substance 
known  as  a  non-conductor  no  current  would  pass,  not  that 
these  substances  do  not  contain  electricity,  because  it  has 
been  shown  that  it  may  be  excited  on  them.  On  the  other 
hand,  if  a  metal  be  rubbed  and  applied  to  the  sensitive 
electroscope  it  will  be  found  to  have  no  effect  on  the  gold- 
leaf,  because,  though  current  is  generated,  it  is  conducted 
away.  A  comparative  list  of  substances  which  are  good, 
poor,  and  non-conductors  of  electricity  can  be  readily 
compiled.  Metals  and  carbon  come  under  the  head  of 
good  conductors;  silver,  copper,  platinum,  iron,  zinc,  and 
mercury  are  the  best.  Poor  conductors  include  water, 
saline  solutions,  acid  solutions,  the  body,  etc.  Non-con- 
ductors include  glass,  vulcanite,  paraffin,  sealing-wax,  dry 
skin,  dry  air,  etc.  Every  conceivable  thing  might  be  in- 
cluded under  one  of  these  heads,  those  mentioned  come 
most  frequently  under  our  notice.  There  is  a  certain 
amount  of  resistance  offered  to  the  passing  of  electricity 
even  by  the  very  best  conductors,  the  comparison  of  the 
conductors  depends  entirely  on  this  property  of  resistance, 
but  even  those  substances  known  as  insulators  convey  a 
certain  amount  of  current.  (The  amount  they  allow  to 
pass  in  some  instances  becomes  dependent  on  the  electrical 
force  which  repels  the  current.) 

During  conduction  of  electricity,  heat  is  always  generated. 
This  property  depends  on  the  amount  of  current  which  is 
passing  and  the  resistance  which  is  afforded. 

From  the  foregoing  it  may  be  concluded  that  there  is 
no  demarcation  between  conductors  and  insulators.  All 
substances  may  be  accounted  conductors,  but  some  con- 
duct so  badly  that  they  are  termed  non-conductors.  Even 
these  are  at  times  affected  by  their  physical  state.  The 
skin,  for  example,  when  perfectly  dry  is  a  very  poor  con- 


24  ELECTRO-PHYSICS 

ductor,  but  when  moistened  is  a  fairly  good  conductor. 
Inversely,  good  conductors  are  similarly  affected  by  their 
physical  state.  Metals  when  heated  become  poorer  con- 
ductors, whereas  heat  increases  the  conductivity  of  carbon. 
Pure  water  does  not  conduct,  but  acidulated  water,  or 
water  to  which  is  added  a  small  quantity  of  salt  becomes  a 
good  conductor.  The  reason  for  these  effects  of  the  physical 
state  on  the  conductivity  of  current  will  be  referred  to 
later.  The  conduction  of  electricity  through  gases  should 
not  be  lost  sight  of,  for  it  has  a  bearing  on  the  action  of  the 
current  in  passing  through  certain  vacuum  tubes  like  the 
x-ray  tube. 

Induction. — It  has  been  stated  that  all  bodies  more  or 
less  contain  electricity,  which  if  it  is  not  manifest  one 
reason  is  that  it  is  evenly  distributed,  and  that  it  may  be 
excited  and  made  manifest  in  different  ways.  The  glass 
rod,  for  example,  contains  electricity,  which  can  be  excited 
by  rubbing  with  silk.  If  the  electrified  glass  rod  is  brought 
near  to  a  suspended  insulated  pith  ball  it  will  attract  it. 
The  explanation  of  this  is  that  the  positively  electrified 
body  brought  in  proximity  of  the  body,  which  contains  a 
certain  amount  of  electricity  evenly  distributed  over  its 
surface,  causes  an  alteration  in  the  distribution  of  elec- 
tricity by  inducing  negative  electricity  to  the  surface  nearest 
to  the  charged  rod,  and  as  unlike  attracts,  the  light  body  is 
drawn  toward  the  electrified  rod.  Induction  takes  place 
whenever  an  electrified  body  is  brought  near  another  body. 
If  an  insulated  substance  is  touched  by  the  electrified  body 
it  will  become  charged  with  electricity  of  the  like  sign, 
but  if  the  electrified  body  be  removed  without  touching, 
the  distribution  of  electricity  in  the  other  becomes  once 
more  evenly  dispersed  over  its  surface.  If  the  insulated 
body  instead  of  being  round  be  pointed  at  each  end,  and 
another  insulated  positively  electrified  body  be  brought 
near  one  end,  it  will  induce  current  of  a  negative  sign  to 
the  point,  where  the  density  will  become  so  great,  that  if 
they  are  brought  close  enough  a  discharge  across  the  inter- 
vening space  in  a  spark  will  take  place,  neutralizing  the 


STATICAL  MACHINES  25 

electrified  body  and  leaving  itself  charged  with  electricity 
of  opposite  sign. 

Statical  Machines. — The  current  produced  by  frictional 
machines  is  the  most  ancient  form  of  procuring  a  continuous 
current  of  electricity  for  therapeutic  purposes.  One  older 
type  of  machine  was  constructed  on  the  principle  of  generat- 
ing a  current  by  friction  of  a  revolving  glass  cylinder  with 
an  amalgamated  leather  rubber.  The  negative  electricity 
generated  on  the  rubber  is  conducted  to  earth  with  the  aid 
of  the  amalgam,  and  the  positive  electricity  on  the  glass 
attracts  a  negative  charge  from  a  stationary  metallic  prime 
conductor  placed  in  close  proximity.  A  negative  charge  from 
the  prime  conductor  neutralizes  the  positive  charged  glass 
cylinder,  and  retains  a  charge  of  positive  electricity,  which 
can  be  conducted  from  the  prime  conductor.  This  form  of 
machine  has  beeen  superseded  by  improved  induction  or 
influence  machines.  One  type,  long  known  and  used,  is  the 
Holtz  machine,  which,  with  the  many  modern  improve- 
ments, is  still  very  popular.  In  this  country  the  Wimshurst 
maclmie  seems  to  be  preferred.  It  has  the  advantages 
of  being  self-exciting,  and  does  not  reverse  the  current 
generated  under  climatic  influences  while  in  action.  "It 
consists  of  two  circular  glass  disks  (or  any  even  number), 
mounted  in  pairs  upon  a  fixed  horizontal  spindle  in  such  a 
way  hat  they  rotate  in  opposite  directions  at  a  distance 
apart  of  not  more  than  a  fraction  of  an  inch.  Each  disk  is 
attached  to  the  end  of  a  hollow  boss  of  wood,  or  of  metal, 
upon  which  is  turned  a  small  pulley.  The  pulleys  are 
driven  by  a  cord  or  belt  from  larger  pulleys  attached  to  a 
spindle  below  the  machine,  and  rotated  by  a  winch  handle 
or  by  a  motor,  the  differences  in  the  direction  of  rotation 
of  the  disks  being  obtained  by  crossing  the  alternating  bits. 
Both  disks  are  well  varnished,  and  attached  to  the  outer 
surface  of  each  these  are  radial  sector-shaped  plates  of 
tin-foil  or  thin  brass  disposed  around  the  disks  at  equal 
angles.  These  sectors  are  not  essential  to  the  action  of  the 
machine  but  they  make  it  more  easily  self-exciting. 

"Twice  in  each  revolution  the  two  sectors  situated  on  the 


26 


ELECTRO-PHYSICS 


same  diameter  of  each  disk  are  momentarily  placed  in 
metallic  connection  with  one  another  by  a  pair  of  fixed 
wire  brushes  attached  to  the  ends  of  a  curved  rod,  called 
the  neutralizing  rod,  supported  at  the  middle  of  its  length 


Fig.  3 


Wimshurst  machine. 


by  one  of  the  projecting  ends  of  the  fixed  spindle  upon 
which  the  disks  rotate,  the  sector-shaped  plates  just  grazing 
the  tips  of  the  brushes  as  they  pass  them. 

"  The  position  of  the  two  pairs  of  brushes  with  respect  to 
the  fixed  collecting  combs  and  to  one  another  is  variable, 


STATICAL  MACHINE  27 

as  each  pair  is  capable  of  being  rotated  on  the  spindle 
through  a  certain  angle,  and  there  is  one  position  of  maxi- 
mum efficiency.  This  position  in  the  machine  appears  to 
be  when  the  brushes  touch  the  disks  on  diameters  situated 
about  75°  from  the  collecting  combs,  and  30°  from  one 
another. 

"The  fixed  conductors  consist  of  two  forks  furnished  with 
collecting  combs  directed  toward  one  another,  and  toward 
the  two  disks  which  rotate  between  them,  the  position  of 
the  two  forks,  which  are  supported  on  ebonite  pillars,  being 
along  the  horizontal  diameter  of  the  disks.  To  these  fixed 
conductors  are  attached  the  terminal  electrodes,  whose 
distance  apart  can  be  varied.  Leyden  jars  are  usually 
fitted  to  the  machine  by  the  makers,  but  these  must  admit 
of  their  outer  coating  being  disconnected,  if  the  machine  is 
to  be  used  for  treating  patients."1  There  are  many  modifica- 
tions of  the  Wimshurst  machine,  some  having  ebonite 
plates,  others  mica  disks.  These  substances  permit  of 
driving  the  machine  at  a  high  speed  without  fear  of  breaking 
the  plates.  All,  however,  are  made  on  the  principle  of  the 
above  description  of  a  frictional  machine  here  quoted. 

1  Lewis  Jones,  Medical  Electricity. 


CHAPTER  II. 
GALVANIC  ELECTRICITY. 

Volta's  Contact  Law — Electrolytes — Voltaic  Cells — Electro-motive  force 
— Practical  Electrical  Units — Resistance — Heat  Effects  of  the  Current — 
Polarization  —  Poles  —  Testing  the  Poles  —  Electrolysis  —  Ions  —  Electro- 
positive and  Electro-negative. 

Galvanic  electricity  is  generated  by  galvanic  or  voltic 
cells  and  by  dynamos.  It  is  the  form  of  current  which  is 
most  used  in  electro-therapeutics.  Its  force  and  current- 
strength  can  be  graduated  and  controlled  at  will.  This 
form  of  current  is  universally  in  use  in  the  world's  commerce, 
for  which  purpose  it  is  generated  by  dynamos.  Thus  it  is 
often  termed  Dynamic  Electricity. 

Discovered  by  Galvani  in  1780  and  improved  in  method 
of  production  by  Volta  in  1800,  it  often  bears  the  names  of 
these  eminent  students. 

Galvanic  electricity  is  produced  when  two  dissimilar  con- 
ductors are  immersed  in  a  liquid  medium,  called  an  elec- 
trolyte, which  has  the  power  of  acting  chemically  on  one 
of  them  more  than  the  other,  and  the  metals  are  joined 
outside  the  liquid;  that  is,  a  circuit  is  formed,  a  continuous 
current  will  flow  between  the  two  metals  within  the  fluid 
and  be  conducted  along  the  plates  and  connecting  wire. 

It  is  necessary  to  dwell  upon  and  study  the  foregoing 
statement  that  two  dissimilar  substances  are  required  to 
form  a  current-producing  cell. 

If  the  metals  or  plates  of  a  cell  are  exactly  alike  or  even 
very  similar  and  are  immersed  into  a  fluid  electrolyte,  which 
is  capable  of  acting  chemically  upon  them,  no  electric 
current  will  be  produced;  for  example,  if  two  zinc  plates  or 
two  copper  plates  are  placed  in  a  solution  of  weak  sulphuric 


GALVANIC  ELECTRICITY  29 

acid  and  the  plates  connected  without  by  wires,  on  testing 
the  wires  connecting  these  similar  plates  no  current  will 
be  found  to  pass,  but  if  a  zinc  plate  and  a  copper  plate 
are  immersed  in  a  similar  acid  solution  and  connected  by 
copper  wire  a  strong  electric  current  will  immediately  flow 
from  the  zinc  to  the  copper  within  the  solution  and  then 
along  the  copper  plate  and  copper  wire  connection  without 
in  a  continuous  circuit. 

Electrolytic  conduction  only  occurs  by  chemical  action 
as  will  subsequently  be  explained,  and  it  is  necessary  that 
the  metals  or  conductors  employed  must  have  different 
affinities  for  oxygen.  This  law  is  observed  in  the  con- 
struction of  all  galvanic  cells. 

The  potential  or  electro-motive  force  depends  on  the 
amount  of  chemical  action  of  the  electrolyte  on  the  sub- 
stances employed,  and  this  potential  difference  is  governed 
by  the  dissimilarity  in  the  chemical  affinities  of  the  plates 
employed.  If,  for  instance,  platinum  and  copper  be  brought 
together  in  a  cell,  the  copper  would  become  positively 
electrified  and  the  platinum  negatively,  and  the  current 
produced  by  such  a  cell  would  be  feeble  compared  to  one 
composed  of  zinc  and  copper,  both  of  which  are  oxidizable, 
the  zinc  in  this  case  being  more  highly  so  becomes  positively 
electrified  and  the  copper  negatively;  the  potential  of  the 
current  from  this  cell  is  much  greater  than  the  other. 

Zinc  is  one  of  the  most  oxidizable  metals  and  most  easily 
acted  upon  by  electrolytes.  It  is  therefore  much  used  in 
the  formation  of  voltic  cells.  Copper,  carbon,  and  silver 
are  very  dissimilar  to  zinc  and  are  often  used  as  negative 
elements  in  the  construction  of  cells  where  zinc  is  the  positive 
element. 

Volta's  Contact  Law. — To  Volta  is  due  the  discovery  of 
the  manifestation  of  difference  in  potential  by  contact  of 
dissimilar  metals  in  air,  and  also,  as  is  known  in  the  con- 
struction of  cells,  that  the  size  or  form  of  the  metals  does 
not  affect  the  potential,  but  only  their  dissimilarity  and  the 
nature  of  the  metals  employed.  The  electro-motive  force 
which  can  be  obtained  by  bringing  together  two  metals  in 


30  ELECTRO-PHYSICS 

an  electrolyte  varies  as  the  degree  to  which  one  becomes 
electro-positive  and  the  other  electro-negative  when  in 
contact. 

Lists  have  been  arranged  according  to  Volta's  contact 
list,  in  which  each  substance  or  metal  in  the  list  will  be 
positively  electrified  when  in  contact  with  any  metal  suc- 
ceeding it,  and  vice  versa,  negatively  electrified  in  contact 
with  anyone  preceding  it  on  the  list.  In  the  list  the  farther 
removed  from  one  another  in  the  series  the  greater  will  be 
the  electro-faction  of  the  metal  if  brought  together  in  con- 
tact; thus  zinc  and  carbon  will  have  a  potential  difference 
far  greater  than  zinc  and  iron. 

Such  a  contact  series  is  as  follows: 

Sodium.  Copper. 

Zinc.  Silver. 

Iron.  Gold. 

Lead.  Platinum. 

Tin.  Carbon. 

According  to  Volta's  contact  law,  "The  difference  of 
potential  between  any  two  metals  is  equal  to  the  sum  of  the 
difference  of  the  potential  between  the  intervening  metals 
in  the  contact  series." 

In  the  construction  of  galvanic  or  voltic  cells  the  metal 
plates  are  usually  chosen  with  due  respect  to  their  differ- 
ence of  potential,  but  other  properties  have  also  to  be 
taken  into  account,  e.  g.,  sodium  is  never  used  although 
between  it  and  carbon  there  is  one  of  the  highest  potential 
differences,  because  it  would  not  be  manageable  for  a  battery. 

The  Electrolyte. — The  electrolyte  of  a  cell  is  the  excitant 
and  conductor  of  current.  It  acts  chemically  on  the  two 
elements  and  conveys  electrically  charged  atoms  from  one 
to  the  other  when  the  current  is  closed. 

Among  the  commoner  fluids  used  as  electrolytes  in  gal- 
vanic cells  are  dilute  sulphuric  acid,  ammonium  chloride, 
persulphate  of  mercury,  etc. 

Voltic  Cells. — To  construct  a  voltic  or  galvanic  cell, 
select  any  two  of  the  dissimilar  metals  from  the  foregoing 


VOLTIC  CELLS 


31 


Fig.  4 


Voltic  cell. 


contact  series,  the  ones  farthest  removed  from  one  another 
will  be  the  most  highly  electrified  when  placed  in  an  electro- 
lyte, which  has  a  greater  chemical  action  on  one  than  the 
other.  Take  zinc  and  copper  for  the  elements  and  sulphuric- 
acid,  immerse  the  two  metals  in  the  acid,  connect  the 
ends  outside  the  vessel  with  wires  (see 
Fig.  4).  As  soon  as  the  contact  is  made 
a  continuous  current  will  flow  from  the 
zinc  through  the  liquid  to  the  copper; 
this  is  the  stronger  current  set  up  by 
establishing  a  potential  difference  be- 
tween the  two  elements — that  is,  elec- 
trifying one  element  positively  and  the 
other  negatively.  The  positive  (  +  ) 
electricity  on  reaching  the  opposite  ele- 
ment is  conducted  by  it  to  the  wire 
connection  without  the  cell,  and  con- 
veyed back  to  the  zinc  again  through 
the  electrolyte,  making  a  complete  circuit,  which  will  go  on 
until  the  electrolytic  strain  on  the  higher  potential  is  re- 
duced to  equilibrium  by  the  ceasing  of  chemical  action  of 
the  electrolyte  on  the  elements,  either  by  their  destruction 
or  by  the  conversion  of  the  oxidizable  surface  through  the 
deposit  of  some  chemical  product  of  a  less  electrostatic  nature. 

The  actual  passing  of  current  through  the  conducting 
fluid  is  effected  by  the  splitting  of  the  H20  molecules  by 
the  electrolytic  effect "  of  the  current  into  hydrogen  and 
oxygen  atoms — ions,  i.  e.,  atoms  carrying  an  electrical 
charge.  The  hydrogen  ions  are  charged  with  positive 
electricity,  and  move  toward  the  copper,  where  they  give 
up  their  charge  of  positive  electricity  to  the  metal  and 
hydrogen  is  liberated.  At  the  same  time  the  oxygen  ions 
move  toward  the  zinc  where  they  give  up  their  charge  of 
negative  electricity,  and  oxygen  is  liberated  or  unites 
chemically  with  the  metal. 

Electro-motive  Force  (E.  M.  F.). — When  electricity  is 
excited  by  the  proximity  of  two  dissimilar  metals  in  an 
electrolyte,  or  by  dynamos  or  by  whatever  means  produced, 


32  ELECTRO-PHYSICS 

that  force  which  sets  the  fluids  in  motion,  that  which 
separates  the  positive  from  the  negative  current  is  called 
electro-motive  force  (E.  M.  F.). 

It  is  that  pressure  or  potential  of  the  current  between 
the  positive  and  negative  poles,  which  always  flows  from 
the  positive  to  the  negative  pole  and  will  continue  in  that 
direction  until  equilibrium  of  pressure  or  potential  is  estab- 
lished. "It  is  that  which  produces,  or  tends  to  produce, 
movement  of  electricity."1  When  we  connect  the  metals 
zinc  and  copper  with  an  exciting  fluid  through  which  current 
may  flow,  that  force  which  causes  the  current  to  move  from 
the  zinc  to  the  copper  within  the  cell  and  to  continue  to 
move  so  long  as  difference  of  potential  exists,  is  electro- 
motive force. 

The  analogy  of  the  flow  of  electric  current  to  that  of  the 
flow  of  water  is  often  made  in  text-books,  the  difference  in 
the  level  of  the  water  being  used  in  the  stead  of  the  difference 
in  the  potential  of  electricity,  the  point  being  there  must 
always  be  a  difference  of  pressure  or  potential  in  order  to 
have  a  flow,  and  the  greater  the  pressure  the  greater  is  the 
flow.  In  thinking  of  this  analogy  of  pressure  resembling 
the  flow  of  water  from  a  higher  to  a  lower  level,  the  thought 
of  the  lesser  current  must  not  be  eliminated,  for  one  kind  of  t 
current  cannot  flow  continuously  without  the  other. 

E.  M.  F.  when  applied  to  a  conductor  like  metal  propels 
continuously  irrespective  of  altitudes  or  position,  from  the 
greater  to  the  lesser  potential;  when  applied  to  an  electrolyte, 
it  is  also  continuous  from  the  positive  to  the  negative. 

The  earth  is  always  electrically  charged,  but  there  is  a 
balance  of  potential  between  the  positive  and  the  negative 
electricity.  The  earth's  potential  is  less  than  any  current 
in  motion,  and  consequently  electricity  in  motion  is  always 
directed  toward  it.  If  we  touch  an  electric  motor  lathe  or 
the  terminals  of  a  switchboard,  which  are  electrically  con- 
nected with  current  from  the  main,  and  at  the  same  time 
make  contact  with  a  gas  or  water  pipe,  which  is  in  good 

1  Ashford,  Electricity  and  Magnetism. 


ELECTRO-MOTIVE  FORCE  33 

contact  with  earth,  the  current  from  the  high  potential 
electrical  source  will  be  conducted  through  the  body  to 
earth,  producing  a  disagreeable  shock. 

In  the  construction  of  voltic  cells  the  electro-motive 
force  varies,  and  depends  not  on  the  size  of  the  cell,  but  on 
the  dissimilarity  of  the  metals  or  "  plates"  which  enter 
into  their  formation.  The  degree  to  which  one  metal 
becomes  more  highly  electrified  than  the  other,  and  that 
tendency  of  the  current  produced  between  the  metals  in  a 
conducting  fluid  to  move  from  the  higher  to  the  lower 
potential  establishes  the  electro-motive  force  of  the  cell. 

The  electro-motive  force  can  be  measured  according  to 
Ohm's  law,  by  ascertaining  the  resistance  and  the  current 
strength  and  multiplying  them  together. 

e  =  CR 
where     .     ...     E  is  the  electro-motive  force 

C  is  the  current  strength, 
and   .     .     .     .     R  is  the  resistance. 

If  we  know  any  two  of  these  factors  we  can  calculate  the 
third  thus: 

If  the  resistance  of  a  cell  and  the  resistance  of  the  ex- 
ternal circuit  are  together  1000  ohms  and  the  current 
strength  is  0.001  ampere  (1  milliampere), 

1000  ohms  X  0.001  ampere  =  1  volt  E.  M.  F. 

In  this  way  we  ascertain  that  the  E.  M.  F.  of  the  cell  is 
1  volt. 

The  current,  the  E.  M.  F.,  and  the  resistance  can  be 
measured  by  suitable  instruments,  which  will  be  described 
in  another  chapter. 

It  has  been  stated  that  the  E.  M.  F.  of  a  cell  depends  on 
the  plates  which  enter  into  its  formation,  and  reference  has 
been  made  to  the  "volt,"  but  it  has  not  been  pointed  out 
what  the  volt  is.  Different  cells,  according  to  the  fore- 
going, vary  in  the  E.  M.  F.,  and  we  require  some  standard 
with  which  to  compare  the  E.  M.  F.  of  cells.1     "The  most 

1  This  is  quoted  from  Ashford's  Electricity  and  Magnetism. 
3 


34  ELECTRO-PHYSICS 

natural  thing  to  do  is  to  take  some  cell,  which  can  easily 
be  set  up,  as  having  unit  E.  M.  F.  But  there  is  a  certain 
E.  M.  F.  which  depends  on  the  fundamental  units,  the 
centimeter,  the  gramme,  and  the  second,  together  with  the 
magnetic  action  of  a  current  of  electricity,  and  it  is  most 
convenient  to  take  this,  or  some  simple  multiple  of  it,  as 
the  unit  of  E.  M.  F.  The  name  given  to  the  practical  unit 
of  E.  M.  F.  is  the  volt,  in  honor  of  Volta. 

"Unfortunately,  no  cell  has  exactly  this  theoretical  E.  M. 
F.,  but  by  careful  experiments  it  has  been  found  that  a 
certain  cell,  called  Latimer  Clark's  Standard,  if  made  up 
accurately  to  a  certain  specification  and  measured  at  a 
temperature  of  15°  C.  has  an  E.  M.  F.  equal  to  1.434  of 
these  theoretical  volts. 

"This  cell,  then,  can  be  used  as  a  standard,  just  as  con- 
veniently as  if  it  had  an  E.  M.  F.  of  1  volt;  other  cells  can 
be  compared  with  it,  and  their  E.  M.  F.  calculated." 

Practical  Electrical  Units. — The  sj^stem  of  measurements 
of  electrical  units  is  based  on  the  scientific  calculation  which 
is  known  as  the  absolute  system.  This  starts  by  taking  the 
unit  of  length,  the  meter,  as  a  definite  fraction  of  the  earth's 
circumference.  The  unit  of  surface  we  obtain  from  this. 
For  the  unit  of  weight  a  smaller  quantity  is  wanted,  and 
the  unit  employed  is  the  weight  of  a  cubic  centimeter  (1 
cubic  meter  =  1,000,000  centimeters)  of  pure  water  at  4°  C. 
(the  temperature  at  which  it  possesses  its  greatest  density 
as  it  expands  again  between  4°  and  0°  C.  For  the  unit  of 
mass  the  gramme,  and  for  the  unit  of  time  the  second  or 
the  centimeter-gramme-second  (C.  G.  S.)  system. 

The  units  with  which  we  are  most  concerned  are  the 
Ohm,  Volt,  Ampere,  Coulomb,  Farad,  and  Watt,  and  these 
are  all  based  on  the  C.  G.  S.  system. 

The  Ohm  is  the  unit  of  resistance  (R).  It  represents  the 
measurement  of  whatever  opposes  the  passing  of  current  in 
any  circuit.  In  calculating  resistance  to  current  produced 
by  a  voltic  cell  the  resistance  opposed  in  circuit  outside  the 
cell  (whether  it  is  only  the  wires  connecting  the  elements  or 
whether  it  is  a  body  in  circuit)   is  estimated  as  external 


PRACTICAL  ELECTRICAL   UNITS  35 

resistance  (R)  and  is  added  to  the  resistance  which  is  offered 
to  passing  of  current  from  one  element  to  the  other  through 
the  electrolyte  within  the  cell  and  through  the  element 
itself  and  termed  internal  resistance  (r). 

The  ohm  is  the  resistance  offered  by  a  column  of  pure 
mercury  106  cm. high  and  1  sq.  mm.  cross-section  at  a  tem- 
perature of  0°  C. 

Resistance  varies  in  different  conductors;  iron  wire,  for 
example,  has  about  six  times  the  resistance  of  copper 
wire. 

The  Volt  (V)  is  the  practical  unit  for  electro-motive  force. 
It  is  the  pressure  that  will  cause  the  current  flowing  through 
1  ohm  of  resistance  to  be  1  ampere. 

The  electro-motive  force  of  the  Daniell  cell  is  sometimes 
used  as  the  standard  unit.  It  is  about  1.079  volts,  but 
varies  with  variations  in  concentration  of  the  solutions  used, 
and  is  consequently  not  as  good  a  standard  to  go  by  as  the 
Latimer  Clark's  cell  (see  p.  34),  but  the  Daniell  cell  is  one 
of  the  best-known  two-fluid  cells  and  is  often  referred  to  as 
the  standard  unit  cell  producing  about  1  volt  electro-motive 
force. 

The  Ampere  is  the  unit  of  current  strength  (C).  It 
represents  the  current  which  is  furnished  by  an  electro- 
motive force  of  1  volt  passing  through  a  resistance  of 
1  ohm.  This  amount  or  quantity  of  current  strength  is 
far  in  excess  of  what  is  required  in  electro-therapeutics. 
It  is  therefore  further  divided  into  one  thousandth  of  an 
ampere  and  termed  the  milliampere  (0.001  ampere). 

The  Coulomb  is  the  unit  of  quantity.  One  coulomb  is 
the  quantity  of  current  which  flows  past  any  point  in  a 
circuit  of  one  ampere  current  strength  for  one  second. 

In  calculating  the  quantity  of  current  which  discharges 
from  accumulators  the  term  ampere-hour  is  used,  which 
indicates  the  quantity  of  current  which  will  be  carried  by 
one  ampere  in  one  hour. 

"The  standard  value  of  the  coulomb  is  equivalent  to 
the  quantity  of  electricity  that  will  flow  through  or  into  a 
body  when  a  current-strength  of  1  ampere  is  maintained 


36  ELECTRO-PHYSICS 

for  one  second,"1  i.  e.,  if  we  are  passing  a  current  of  5 
milliamperes  through  a  patient  for  20  minutes  the  number 
of  coulombs  that  have  been  applied  is 

0.005  X  20  X  60  =  6. 

The  Farad  is  the  unit  of  capacity.  It  is  that  capacity 
which  would  require  1  coulomb  to  charge  it  to  1  volt.  A 
condenser  which  is  of  a  given  capacity  must  contain  a 
given  area  of  metallic  conductor  lining  to  charge  it  to  the 
potential  of  1  volt. 

The  Watt  is  the  unit  of  electric  power.  It  is  the  volt- 
ampere.  A  current  of  1  ampere  with  a  potential  of  1 
volt  has  a  power  of  1  watt,  or  a  proportionately  smaller 
current  strength  and  greater  electro-motive  force  will 
produce  the  same  power;  for  example,  Yt  ampere  and  10 
volts  will  produce  one  watt.  The  number  of  watts  is 
determined  by  multiplying  the  number  of  amperes  by  the 
volts.    736  watts  are  equal  to  one  horse-power. 

Resistance. — It  has  been  stated  that  conductivity  of 
electricity  by  solids  varies  greatly  with  the  nature  of  the 
material.  Resistance  may  be  said  to  be  the  inverse  to 
conduction.  Metals  are  accounted  the  best  conductors, 
but  however  good  the  conductors  an  amount  of  resistance 
is  encountered  on  the  passing  of  electric  current.  The 
amount  of  resistance  varies  according  to  the  kind  of  con- 
ductor, the  nature  of  the  material  has  an  influence  on  the 
resistance;  certain  pure  metals,  which  offer  least  resistance 
to  current  are  changed  by  being  alloyed.  Copper,  for 
instance,  offers  little  resistance  to  current,  but  when  alloyed 
to  form  German  silver  (copper  60  parts,  zinc  26,  nickel 
14)  has  a  high  resistance. 

The  resistance  varies  directly  as  the  length  and  inversely 
as  the  square  of  the  diameter. 

A  metal  wire  of  a  given  length  has  twice  the  resistance  of 
a  similar  wire  of  half  that  length;  so,  too,  if  the  diameter 

1  Dawson  Turner,  Practical  Medical  Electricity. 


RESISTANCE  37 

of  a  given  length  of  a  conductor  be  increased  by  twice,  the 
resistance  will  be  reduced  to  one  quarter  the  other. 

The  resistance  of  metal  conductors  is  therefore  dependent 
in  individual  cases  on  the  nature  of  the  material,  the  length, 
and  diameter. 

With  the  exception  of  a  few  alloys,  raising  the  temperature 
increases  the  resistance  of  metals;  the  resistance  of  carbon 
is  decreased  with  raising  the  temperature. 

A  table  of  resistance  of  metals  in  comparison  of  a  similar 
length  and  thickness  would  work  out  as  follows: 

Silver 1.00 

Copper 1 .  06 

Gold 1.38 

Aluminium 1.94 

Platinum 6.08 

Iron 6.80 

Lead 13.60 

Mercury       .      .      .     ' 62.50 

If  the  resistance  of  a  given  length  of  silver  wire  of  a 
given  thickness  be  ascertained,  the  resistance  of  any  of 
the  others  may  be  calculated  from  this  table. 

The  conduction  of  liquids  excepting  mercury  is,  as 
has  been  explained,  of  quite  a  different  nature;  some  are 
almost  non-conduc  ors  of  current,  as  oils  for  instance. 

In  passing  a  current  through  a  liquid  resistance,  as  in 
the  electrolyte  of  a  cell,  decomposition  takes  place.  The 
body  comes  under  the  heading  of  liquid  conductors,  and 
various  tissues  and  liquids  in  its  composition  have  a  greatly 
varying  resistance. 

To  calculate  the  resistance  the  current  meets  in  an  electric 
circuit  derived  from  a  cell,  the  internal  resistance,  that  is, 
resistance  met  chiefly  in  the  electrolyte  within  the  cell 
between  the  exciting  plates,  must  be  taken  into  account 
and  added  to  the  external  resistance,  which  is  the  resistance 
met  in  the  metallic  conducting  wires,  and  whatever  body 
is  interposed  between  the  two  terminals  or  poles. 

To  calculate  resistance,  current  strength  and  electro-motive 
force  it  is  necessary  to  have  a  clear  conception  of  the  law 


38  ELECTRO-PHYSICS 

laid  down  by  Ohm,  which  deals  with  the  relation  of  force 
or  potential  to  current  strength  and  resistance. 

Ohm's  Law. — "The  strength  of  the  current  in  any  cir- 
cuit or  part  of  a  circuit  varies  directly  as  the  electro- 
motive force  in  that  circuit,  and  inversely  as  the  resistance 
of  the  circuit." 

To  clearly  understand  this  law  examples  of  its  equations 
explain  it  more  fully. 

Let  E  stand  for  electro-motive  force  in  volts,  C  for 
current  strength  in  amperes,  and  R  for  resistance  in  ohms. 

E 

Current  strength  =  — 
R 

Electro-motive  force  =  CR 

T,       •  E 

Resistance  =  — 

From  these  equations  it  is  easy  to  calculate  C,  E,  or  R 
by  a  simple  algebraic  sum.  To  find  the  current  strength 
(C)  when  E.  M.  F.  is  known  to  be  18  volts  and  R  1500 
ohms: 

18 
C  =  — —  =  0.012  (amperes)   =  12  milliamperes. 

To  find  electro-motive  force  when  R  is  200  ohms  and 
C  is  0.008  amperes: 

E  =0.008  X  2000  =  16  volts. 

To  find  resistance  when  E  is  18  volts  and  C  is  0.006 
amperes : 

18 

R  =  oToo6=3000ohms- 

The  practical  application  of  Ohm's  law  contributes  to 
our  proper  understanding  of  much  we  have  to  study  in 
electro-physics.  In  practice  much  interest  is  added  to  our 
electro-therapeutics  by  calculating  the  resistance  of  different 
patients,  and  it  will  be  found,  if  this  is  done,  that  resistance 


HEAT  EFFECTS  OF  THE  CURRENT  39 

of  the  body  varies  in  a  remarkable  manner  in  different 
patients. 

Heat  Effect  of  the  Current. — One  of  the  effects  by  which 
the  presence  of  current  can  be  ascertained  in  passing  through 
a  conductor  is  the  heat  produced.  The  amount  of  heat 
produced  may  not  be  sufficient  appreciably  to  raise  the 
temperature,  but  if  the  current  is  sufficiently  large  and 
resistance  high  enough,  in  time  the  temperature  of  the  con- 
ductor will  be  raised  to  appreciable  heat  or  even  red  or 
white  heat.  The  quantity  of  heat  produced  by  the  pass- 
ing of  a  definite  current  through  a  definite  resistance  in  a 
given  time  has  been  calculated  by  Joub,  who  formulated 
a  law  which  says  that  "the  number  of  units  of  heat  gener- 
ated by  a  current  in  a  conductor  is  proportional  (1)  to  its 
resistance,  (2)  to  the  square  of  the  strength  of  the  current, 
(3)  to  the  time  during  which  it  flows."  From  this  law  can 
be  calculated  the  quantity  of  heat  produced  when  a  given 
current  flows  through  a  circuit  with  a  given  resistance  in 
a  given  time.  The  energy  absorbed  by  the  resistance  of 
the  circuit  is  dissipated  in  the  form  of  heat.  The  energy 
utilized  in  the  production  of  heat  is  dependent  on  the 
resistance  of  the  conductor.  Thus  when  we  want  to  pro- 
duce great  heat,  as  in  a  cautery,  a  strong  current  strength 
is  passed  through  a  small  area  and  length  of  platinum 
wire  which  affords  a  great  deal  of  resistance.  If  a  good 
conducting  wire  like  silver  is  used,  the  resistance  of  which 
is  one-sixth  that  of  platinum,  a  much  greater  current 
strength  will  be  required  to  heat  the  wire  to  redness.  The 
part  resistance  plays  in  respect  to  energy  in  the  production 
of  heat  when  a  current  is  passed  through  different  con- 
ductors may  be  amplified  by  the  experiment  of  passing  a 
current  through  a  small  chain  consisting  of  alternate  links 
of  platinum  and  silver,  when  the  current  is  sufficient  to 
produce  red  heat  in  the  platinum  links,  the  silver  links 
will  remain  unheated  perceptibly. 

The  resistance  of  the  filament  of  an  incandescent  lamp 
has  to  be  great,  and  the  production  of  light  is  in  consequence 
of  the  raising  of  the  temperature  to  white  heat  in  a  vacuum, 


40  ELECTRO-PHYSICS 

the  resistance  required  and  the  current  employed  being 
dependent  on  the  E.  M.  F.  and  the  candle  power  of  the 
lamp. 

The  heating  properties  of  the  current  passing  through  a 
wire  of  small  dimensions  and  known  resistance  has  been 
utilized  in  construction  of  hot-wire  instruments  for  the  meas- 
urement of  alternating  and  high-frequency  currents,  where 
magnetic  instruments  would  be  useless.  Milliampere  meters 
are  constructed  for  this  purpose  on  the  principle  of  heating; 
by  the  passage  of  the  current  a  fine  platinum  wire  is  heated 
and  by  expansion  caused,  a  pointer  attached  is  rotated  over 
a  scale  which  indicates  the  current. 

In  the  practical  use  of  the  current  the  heating  effect 
can  be  noticed  when  the  author's  method  of  bleaching 
dead  teeth  is  carried  out.  If  two  fine  platinum  wires  are 
inserted  at  two  points  in  the  dentine  and  the  bleaching 
agent  interposed  as  the  conductor  and  completer  of  the 
circuit,  when  current  strength  of  over  10  milliamperes  is 
passing,  the  whole  structure  of  the  crown  of  the  tooth 
becomes  perceptibly  heated,  and  if  the  current  strength  is 
raised  for  a  minute  or  two  to  15  milliamperes  the  heat 
becomes  intolerable  to  the  patient. 

One  of  the  effects  of  general  electrization  by  high-frequency 
currents  is  the  production  of  heat,  an  increase  of  the  surface 
temperature  of  the  body  frequently  takes  place  and  the 
patient  feels  warm. 

D'Arsonval  has  shown  that  under  the  influence  of  auto- 
conduction  the  heat  given  off  from  the  body  is  greatly 
increased. 

Polarization. — This  term  is  applied  to  an  obstructing  of  the 
current  in  chemically  formed  cells  and  has  to  be  reckoned 
with  in  considering  the  resistance  to  current  within  the 
cell.  It  is  brought  about  by  an  alteration  of  the  surface  of 
the  plates  of  the  cell  during  the  chemical  action  which 
excites  the  flow  of  current,  usually  by  the  accumulation  of 
hydrogen  gas  on  the  negative  plate.  Take,  for  example,  a 
simple  galvanic  cell  composed  of  zinc  and  silver  with  an 
electrolyte  of  ammonium  chloride;  on  closing  the  circuit 


POLARIZATION— POLES  41 

electricity  flows  within  the  cell  from  the  zinc  to  the  silver 
and  electrolysis  takes  place,  the  hydrogen  ions  pass  to  the 
silver  plate,  discharge  their  current  to  the  conducting 
metal,  and  hydrogen  gas  accumulates  on  the  surface  of  the 
plate  which  it  coats  with  bubbles.  These  bubbles  act  as  a 
buffer  or  resistance  to  further  electrolytic  action.  At  the 
same  time  oxygen  ions  migrate  to  the  zinc  plate,  discharge 
their  electric  charge,  and  act  chemically  on  the  zinc  to 
form  oxide  of  zinc.  The  polarization  of  the  silver  plate  by 
the  coating  of  hydrogen  bubbles  on  its  surface  changes  that 
element  from  one  of  dissimilarity  to  the  zinc  to  practically 
one  of  great  similarity;  the  relative  potential  is  altered.  This 
is  opposed  to  Volta's  contact  law,  which  says  that  in  order 
to  produce  flow  of  current  it  is  necessary  to  connect  two 
dissimilar  elements  in  an  electrolyte. 

To  overcome  polarization  in  cells,  makers  devise  different 
methods  to  eliminate  the  gases  or  neutralize  the  chemical 
product  which  accumulates  on  the  plates  during  the  work- 
ing of  the  cells.  This  is  called  depolarization.  It  may  be 
accomplished  to  a  certain  extent  by  mechanical  means, 
but  the  method  most  commonly  used  is  the  introduction 
of  some  chemical  which  by  its  affinity  for  the  polarizing 
product  unites  with  it  to  form  some  other  product  which 
does  not  affect  the  action  of  the  cell,  and  rids  the  plates 
of  the  polarizing  effect.  The  depolarizer  lessens  the  internal 
resistance  of  the  cell,  which  would  increase  as  the  current 
continued  to  flow  and  the  E.  M.  F.  would  gradually  fall. 
Hydrogen  gas  on  the  negative  element  is  the  most  frequent 
polarizing  product  of  a  cell  and  the  method  of  depolarizing 
is  generally  a  chemical  one,  by  the  presence  of  some  oxi- 
dizing agent  which  unites  with  the  hydrogen  as  fast  as  it 
appears  on  the  surface  of  the  plates.  In  the  Leclanche 
cell,  manganese  peroxide  is  the  depolarizer;  in  bichromate 
of  potash  cell,  chromic  acid;  in  the  persulphate  of  mercury, 
persulphate  of  mercury. 

Poles. — In  all  chemical  cells  the  flow  of  current  is  from 
the  positive  (  +  )  element  to  the  negative  (  — )  within  the 
cell;  that  is,  from  the  greater  potential  to  the  lesser,  but  it 


42 


ELECTRO-PHYSICS 


must  not  be  forgotten  that  there  is  also  a  weaker  current 
which  flows  in  the  opposite  direction  from  (  — )  to  (+). 
When  the  current  of  higher  potential  (+)  passing  through 
the  electrolyte  reaches  the  negative  (  — )  element  it  is 
conducted  by  it  outside  the  cell  to  the  end  which  is  called 
the  terminal;  therefore  the  negative  element  without  the  cell 
becomes  the  positive  pole,  because  it  conveys  the  current 
of  higher  potential,  and  the  positive  element  becomes  the 
negative  pole.      A  study  of  the  accompanying  illustration 

Fig.  5 


Direction  of  current  inside  and  outside  cell. 


will  serve  o  explain  how  the  current  flowing  in  a  closed 
circuit  from  a  cell  has  the  +  pole  at  the  terminal  of  the 
negative  element. 

Testing  the  Poles. — The  chemical  action  at  the  + 
pole  in  a  circuit  is  acid  and  at  the  —  pole  alkaline;  that  is, 
when  current  flows  through  a  liquid  separating  the  terminals 
in  the  circuit.  Many  simple  tests  which  are  useful  in  deter- 
mining the  poles  are  based  on  the  acidity  and  alkalinity  of 
the  respective  poles. 

To  find  the  poles:  1.  Moisten  a  slip  of  blue  litmus 
and  place  it  on  a  glass  slab,  apply  the  electrodes  conveying 


TESTING  THE  POLES  43 

current  from  two  poles  of  a  battery  or  whatever  source  of 
electricity,  about  3  cm.  apart,  the  paper  will  turn  red  at 
the  +  pole. 

2.  A  few  drops  of  phenol-phthalein  (a  clear,  colorless 
liquid)  in  a  glass  of  water  and  two  metal  electrodes  placed 
3  or  4  cm.  apart  in  the  water,  with  a  current  in  circuit,  will 
give  a  bright  purple  coloring  to  the  water  about  the  —  elec- 
trode. The  commonly  employed  testing  paper  is  paper 
impregnated  with  this  solution. 

3.  A  simple  and  convenient  method  is  to  immerse  the 
wires  from  the  terminals  of  the  cell  in  water  containing  a 
little  salt  or  acid ;  a  few  small  bubbles  collect  on  the  positive 
pole  and  tend  to  stick  to  it  and  grow  larger,  while  a  number 
of  minute  bubbles  collect  on  the  negative  pole  and  tend  to 
leave  it  rapidly  and  rise  to  the  surface  of  the  liquid. 

One  of  these  tests  is  often  a  handy  means  of  determining 
the  poles  when  dealing  with  current  from  the  main,  in 
using  a  switchboard,  even  though  the  poles  are  marked; 
the  plug  connecting  the  board  may  become  reversed  and 
the  identity  of  the  poles  lost.  A  milliampere  meter  attached 
to  a  switchboard  is  always  an  indicator  of  the  constancy 
of  the  poles;  if  the  plug  is  reversed  the  current  in  passing 
through  the  instrument  will  deflect  the  needle  in  the  opposite 
direction  to  that  marked  on  the  terminal  on  the  board, 
indicating  the  change  in  direction  of  the  flow  of  current. 

Electrolysis. — It  has  been  pointed  out  that  when  two 
dissimilar  elements  are  connected  in  an  electrolyte  or 
exciting  fluid,  a  current  flows  from  the  positive  to  the 
negative  element  within  the  cell  and  that  a  chemical  action 
takes  place  wi  hin  the  cell. 

A  similar  chemical  action  takes  place  when  current 
collected  from  a  cell  or  other  source  of  electricity  is  passed 
through  a  liquid  or  compound  or  tissue  outside  a  cell  or 
other  electrical  source  of  current  supply,  between  the  two 
terminals. 

If  we  place  two  platinum  electrodes  in  a  vessel  con- 
taining water  and  pass  current  through  the  water,  bubbles 
of  gas  will  rise  from  each  electrode  which  will  be  found  to 


44  ELECTRO-PHYSICS 

be  oxygen  at  the  positive  and  hydrogen  at  the  negative 
electrode,  the  formation  of  these  gases  would  take  place 
exceedingly  slowly,  hardly  at  all,  because  pure  water  is 
almost  a  non-conductor  of  current,  and  is  only  mentioned 
here  as  an  example  of  the  splitting  of  a  liquid  by  the  action 
of  the  current. 

Electrolysis  may  be  defined  as  "the  process  of  splitting 
up  a  liquid  chemically  by  passing  an  electric  current  through 
it."  The  liquid  is  the  electrolyte,  the  positive  electrode  is 
called  the  anode  and  the  negative  electrode  the  cathode. 

Now  if  the  water  in  the  foregoing  experiment  contains 
a  salt  in  solution  it  becomes  a  good  conductor  of  electricity 
and  the  electrolytic  action  is  greatly  increased.  The  action 
of  the  current  on  a  large  class  of  compounds  dissolved  in 
water  or  other  solvent  may  be  explained  by  taking  one 
of  the  simplest  salts,  sodium  chloride  (NaCl)  for  example, 
which  in  the  solid  state  consists  of  molecules  composed  of 
one  atom  of  sodium  and  one  of  chloride,  when  dissolved 
in  water  a  certain  number  of  the  molecules  dissociate  into 
atoms  of  sodium  and  chlorine,  these  atoms  move  about  in 
the  solution  in  no  regular  formation  and  with  no  particular 
destiny,  and  are  the  ions  when  electricity  is  passed  through 
the  solution. 

The  effect  of  the  current  on  such  a  solution  is  to  cause 
decomposition  of  the  solution  (or  electrolyte),  the  molecule 
NaCl  is  split  or  dissociated  into  the  ion  Na,  which  becomes 
positively  charged  and  the  ion  CI  which  becomes  negatively 
charged.  The  charge  of  current  is  equal  in  each  case. 
The  positively  charged  ion  moves  toward  the  negative  elec- 
trode and  the  negatively  charged  ion  toward  the  positive 
electrode.  In  this  manner  electric  current  passes  through 
the  electrolyte,  the  ions  conveying  definite  charges  of  elec- 
tricity, and  oxygen  is  liberated  at  the  anode  and  hydrogen 
at  the  cathode. 

But  in  the  case  of  an  electrolyte  containing  a  salt  and 
an  alkali  metal,  the  action  is  often  far  more  complicated; 
it  may  be  found  that  when  the  molecule  is  split  one  of  the 
electrically  charged  atoms  is  composed  of  a  chemical  com- 


ELECTROLYSIS  45 

pound  of  an  unknown  composition,  in  which  case  the  atom 
may  combine  with  one  of  the  atoms  of  water  to  form  a 
new  chemical  compound. 

Take,  for  example,  copper  sulphate,  CuSo4,  if  this  is 
electrolyzed  between  'platinum  electrodes,  the  Cu  ion  moves 
to  the  cathode  and  copper  is  deposited  on  the  platinum 
and  hydrogen  is  liberated,  the  So4  ion  (which  is  called  sulph- 
ion, but  is  not  a  chemical  compound)  moves  to  the  anode, 
where  it  unites  with  some  of  the  water  (H20)  to  form  sul- 
phuric acid  (H2S04)  and  oxygen  is  liberated. 

If  the  same  salt  is  electrolyzed  between  copper  electrodes 
there  is  a  further  effect  produced,  another  reaction  takes 
place,  the  sulphion  (SO3)  instead  of  uniting  with  the  H2 
atom  of  water,  attacks  the  copper  anode  and  forms  copper 
sulphate  (CuS04)  after  giving  up  its  charge  of  electricity 
to  the  electrode,  and  the  metal  is  in  the  course  of  time 
reduced  in  weight  by  the  loss  of  copper  ions  which  go  into 
the  electrolyte  and  replenish  it.  At  the  same  time  the 
copper  ion  (Cu)  is  deposited  on  the  cathode  after  giving 
up  its  charge  of  electricity,  and  this  electrode  is  increased 
in  weight  at  the  expense  of  the  other. 

If  sodium  sulphate  (NaSo4)  is  electrolyzed  between 
platinum  electrodes  a  still  further  effect  will  be  produced. 
There  will  be  a  secondary  action  at  both  electrodes.  The 
following  action  takes  place,  the  sodium  sulphate  is  split 
into  sodium  and  sulphion,  the  sodium  (Na)  ions  become 
positively  charged  and  move  toward  the  cathode,  where 
the  electric  charge  is  given  up  and  the  sodium  unites  with 
hydrogen  of  the  water,  forming  sodium  hydrate  and  liberat- 
ing hydrogen;  the  sulphion  (So4)  becomes  negatively  charged 
and  moves  toward  the  anode,  where  the  electric  charge  is 
given  up  and  sulphion  (So4)  unites  with  the  water  (H20)  to 
form  sulphuric  acid  (H2SOi)  and  oxygen  (0)  is  liberated.  If 
to  this  solution  some  neutral  litmus  is  added  before  electro- 
lyzing  it  a  blue  reaction  will  appear  at  the  cathode  and  red 
at  the  anode,  indicating  alkalinity  at  the  cathode  and 
acidity  at  the  anode. 

The  quantitative  results  of  electrolysis  were  determined 


46  ELECTRO-PHYSICS 

by  Faraday,  who  by  experiments  discovered  the  relative 
quantities  of  substances  liberated  at  the  electrodes.  He 
found  that  when  the  current  is  passed  through  a  series  of 
voltameters  (or  electrolytic  cells)  with  the  same  electro- 
lytes and  the  same  electrodes  that  the  weight  of  the  product 
of  electrolysis  in  each  cell  was  the  same,  but  when  the 
electrolytes  and  the  electrodes  were  different  the  product  of 
electrolysis  varied  according  to  the  chemical  equivalent 
quantities;  he  therefore  formulated  the  law:  "When  a 
current  passes  through  different  electrolytes  in  series  the  ratio 
between  the  quantities  of  the  substances  appearing  at  the 
electrodes  is  the  same  as  that  of  their  chemical  equivalents. " 
A  simple  but  clear  explanation  of  this  law  is  here  quoted 
from  Ashford  as  follows:  "Suppose  that  a  current  passes 
through  two  cells  in  series  containing  respectively  (A) 
acidulated  water,  (B)  copper  sulphate  solution,  both  with 
platinum  electrodes,  and  a  third  (C)  containing  copper, 
sulphate  solution  with  copper  electrodes.  Suppose  that 
the  current  is  allowed  to  flow  until  1  gram  of  hydrogen 
has  been  liberated  in  A.  To  form  the  water  in  A,  8  grams 
of  copper  are  combined  with  each  gram  of  hydrogen,  so 
that  8  grams  of  oxygen  are  liberated  at  the  anode  in  A,  and 
therefore  also  at  the  anode  at  B.  Now  31.7  grams  of  copper 
are  chemically  equivalent  to  8  grams  of  oxygen  so  that  31.7 
grams  of  copper  will  be  deposited  on  the  cathode  in  B  and 
therefore  also  in  C.  Thus  from  Faraday's  results  we  see 
that  the  following  quantities  are  simultaneously  liberated: 
Hydrogen  1,  oxygen  8,  copper  31.7.  These  numbers  are  the 
chemical  equivalents  of  these  elements." 

Ions. — In  the  section  on  electrolysis  it  was  stated  that 
the  action  of  the  current  in  an  electrolyte  is  to  split  it  up 
chemically  into  simpler  materials  which  move  to  their 
respective  electrodes.  The  term  ions  is  given  to  those 
materials,  that  which  travels  to  the  anode  is  called  the 
anion,  that  which  goes  to  the  cathode  the  cation.  (The 
terms  anion  and  cation  although  often  used  in  reference  to 
ionization  are  very  misleading  and  difficult  to  construe  and 
will  be  seldom  used  here,  to  avoid  confusion.) 


IONS  47 

The  ion  is  the  conveyer  of  electricity.  It  is  the  product 
of  a  splitting  up  of  the  component  parts  of  a  compound 
and  is  associated  with  the  idea  of  something  material  which 
moves  or  is  going  in  some  direction. 

Salts  are  formed  by  the  chemical  union  of  metals  or 
metallic  radicals  with  acid  radicals;  when  a  current  is 
passed  through  an  electrolyte  containing  a  salt  in  solution, 
the  metals  or  metallic  radicals  move  from  the  anode  to  the 
cathode  (hydrogen  is  included  in  these)  and  the  acid  radicals 
always  move  in  the  opposite  direction,  i.  e.,  from  the  cathode 
to  the  anode.  Those  atoms  which  are  split  by  the  electro- 
lytic action  of  the  current  are  the  ions  which  carry  definite 
charges  of  electricity  and  are  set  free  at  the  respective 
electrodes  to  which  they  migrate.  In  the  case  of  acids  in 
the  composition  of  an  electrolyte  they  act  like  salts  whose 
metal  is  hydrogen;  thus  in  hydrochloric  acid,  hydrogen 
will  appear  at  the  cathode  and  chloride  at  the  anode. 

Bases  act  like  salts  whose  acid  is  hydroxyl  (OH).  Thus 
in  potassium  hydrate  (KOH)  the  (K)  potassium  becomes 
positively  charged  and  will  appear  at  the  cathode  and  the 
(OH)  hydroxyl  becomes  negatively  charged  and  will  appear 
at  the  anode. 

Leduc  in  explaining  the  migration  of  ions  says:  "The 
fragments  resulting  from  the  dissociation  of  molecules  are 
the  ions,  and  these  ions  are  carriers  of  electric  charges, 
to  which  the  electrolytic  conduction  is  due.  The  anions 
carry  negative  charges,  and  are  consequently  attracted 
by  the  positive  electricity  of  the  anode.  The  cations 
carry  positive  charges:  they  are  repelled  by  the  anode  and 
attracted  by  the  negative  electricity  in  contact  with  the 
cathode.  On  coming  in  contact  with  the  electrode,  the 
ions  are  unloaded,  neutralizing  quantities  of  electricity 
equal  to,  and  of  opposite  sign  to  themselves;  and  these 
quantities  of  electricity  will  be  replaced  by  new  charges 
coming  from  the  generator,  and  it  is  thus  that  the  electric 
current  is  produced   and   maintained. 

"  Plurovalent    ions    carry    electric    charges    proportioned 


48  ELECTRO-PHYSICS 

to  their  valency;  or  rather  it  is  the  electric  charges  which 
determine  the  valency."1 

The  rate  of  movement  of  ions  in  an  electrolyte  varies 
according  to  the  electro-motive  force  and  the  direction  of 
migration  of  the  ions,  those  conveying  positive  charges 
moving  faster  than  the  negatively  charged  ions.  "Hottorf 
has  shown  that  the  velocity  of  anions  differs  from  that  of 
cations.  This  may  be  proved  by  the  following  experiment: 
A  solution  of  sulphate  of  copper  is  placed  in  an  electrolyte 
cell  with  a  porous  partition,  the  solution  being  identical 
on  both  sides  of  the  partition.  After  passing  a  current 
for  some  time  the  solution  is  found  to  be  more  concentrated 
on  one  side  of  the  partition.  The  anion  S04  has  traveled 
faster  than  the  cation  CU,  although  the  number  of  ions 
liberated  at  the  electrodes  is  the  same 


I  S04  S04  SO*   I  SO4  S04  S04  I 
-   1  CU  CU  cu  I  CU  CU  cu  I    + 

Before  the  passage  of  current. 


S04     I     SO4    S04    S04    SO4    SO4     I 

-  1  CU  CU  CU  cu  1  CU  cu I   + 

After  the  passage  of  current. 


"The  ratio  of  the  degree  of  concentration  on  either  side 
of  the  porous  diaphragm  enables  us  to  estimate  the  relative 
velocities  of  the  anions  and  cations,  respectively."2 

This  experiment  is  also  alluded  to  by  Leduc,  who  points 
out  that  "Three  ions  are  liberated  at  each  electrode,  but 
in  consequence  of  the  difference  of  the  speed  of  the  ions 
the  negative  half  of  the  cell  does  not  contain  more  than 
one  molecule  of  sulphate  of  copper,  having  lost  two-thirds 
of  its  concentration,  while  the  positive  half  contains  two 
parts,  having  lost  only  one-third  of  its  concentration.    It  is 

1  Leduc,  Electric  Ions  and  Their  Use  in  Medicine. 

2  Guilleminot,  Electricity  in  Medicine. 


IONS  49 

easy  to  conclude  from  this  that  the  ions  move  in  opposite 
directions  at  different  rates." 

The  rate  of  travel  and  the  depth  of  penetration  of  ions 
when  the  electrolyte  is  a  moistened  tissue  depends  in  a 
measure  on  the  current  strength  and  resistance  offered  in 
the  particular  tissue;  that  is,  the  molecular  conductivity 
of  the  kind  of  electrolyte  will  influence  the  passing  of  ions, 
and  this  must  be  considered  in  their  practical  application; 
a  liquid  will  convey  ions  at  a  rapid  rate  with  little  resistance, 
whereas  gelatinous  substances  or  a  tissue  will  retard  the 
rate  of  travel.  The  kind  of  tissue,  whether  a  good  electro- 
lyte or  an  indifferent  one,  will  influence  the  speed  and  pene- 
tration of  ions.  The  penetration  will  also  be  considerably 
affected  by  the  changes  the  ions  undergo  when  they  enter 
the  tissue.  Soma  are  precipitated  at  once  and  only  remain 
in  the  superficial  layers,  while  others  can  be  driven  in  to  a 
great  depth. 

A  simple  ionic  effect  is  furnished  when  the  current  is 
passed  through  an  aqueous  solution  of  zinc  chloride,  the 
zinc  chloride  molecules  are  dissociated  by  the  effect  on  the 
solution,  zinc  ions  charged  with  positive  electricity  migrate 
toward  the  negative  electrode  white  the  CI  ions  become 
charged  with  negative  electricity  and  migrate  in  the  oppo- 
site directions. 

A  practical  but  more  complicated  illustration  is  found 
in  gold  plating,  a  process  carried  out  in  most  dental  labora- 
tories. Here  the  electrolyte  is  cyanide  of  gold  (8  KCN 
+  4  Au  +  02  +  2H20) ,  the  positive  electrode  is  a  piece  of 
pure  gold  (anode),  the  negative  electrode  is  the  piece  to 
be  plated  (cathode),  which  may  be  gold,  silver,  copper, 
german  silver,  etc.  By  the  electrolytic  effect  the  solution 
is  split  into  Au  ions  charged  with  positive  electricity,  which 
migrate  toward  the  negative  electrode  to  which  they  give 
up  their  charge  of  positive  electricity  and  on  which  gold  is 
deposited,  at  the  same  time  the  dissociated  KCN  ions 
migrate  toward  the  positive  electrode  (gold)  where  they 
give  up  their  charge  of  negative  electricity,  and  here  one 
of  the  complicated  electrolytic  effects  takes  place.  The 
4 


50 


ELECTRO-PHYSICS 


KCN  atoms  unite  chemically  with  02  and  the  gold  elec- 
trode to  form  gold  cyanide  which  replenishes  the  solu- 
tion with  gold  atoms.  The  atoms  in  the  charged  state  are 
supposed  to  take  on  a  regular  formation  and  to  migrate 
to  their  respective  directions  (Fig.  6).  The  velocity  of 
migration  of  the  gold  ions  varies  with  the  drop  in  voltage 
and  consequently  with  the  current  strength  and  also  with 
the  temperature  of  the  electrolyte.  If  we  desire  to  plate 
a  piece  with  a  thick  coating  of  gold  we  use  a  strong  current 
with  a  solution  rich  in  gold  ions  and  raise  the  temperature 
slightly. 

Fig.  6 


Battery 


The  supposed  migration  of  ions. 

The  gas  bubbles  which  collect  at  the  electrodes  are  H2 
at  the  cathode  and  O  at  the  anode,  which  are  ions  of  the 
molecule  H20  charged,  dissociated,  and  migrated  in  pre- 
cisely the  same  manner  as  the  other  ions  of  this  compound 
solution. 

Electro-positive  and  Electro-negative. — From  the 
foregoing  it  has  been  pointed  out  that  the  action  of  the 
current  on  molecules  of  salts  in  solution  is  to  split  up  the 
component  parts  into  ions,  which  become  positively  and 
negatively  charged  and  move  in  the  direction  of  attraction 
of  the  particular  ion,  or,  in  another  sense,  to  be  repelled  from 


ELECTRO-POSITIVE  AND  ELECTRO-NEGATIVE     51 

one  pole  toward  the  other.  The  ions,  which  are  positively 
charged,  are  repelled  from  the  positive  pole  and  carry  a  posi- 
tive charge  of  current  with  them,  these  are  termed  electro- 
positive. Those  which  are  negatively  charged  are  repelled 
from  the  negative  pole  and  are  called  electro-negative. 

An  example  of  electro-positive  and  electro-negative 
elements  in  an  electrolyte  conducting  current  is  often 
experienced  in  the  mouths  of  patients  whose  approximating 
surface  of  teeth  are  filled  with  two  dissimilar  metals;  take, 
for  instance,  two  premolars,  the  posterior  approximal  sur- 
face of  the  first  filled  with  amalgam  and  the  anterior  ap- 
proximal of  the  second  filled  with  gold,  both  fillings  ex- 
tending to  the  cervical  margin,  the  secretions  of  the  mouth 
provide  an  excellent  electrolyte.  In  these  cases  if  the 
metals  are  slightly  in  contact  at  the  articulating  surfaces 
of  the  fillings  a  perfect  cell  is  formed  and  current  strength 
which  is  produced  by  such  a  cell  is  considerable — quite 
sufficient  to  cause  considerable  pain  if  the  pulps  are  alive. 
It  is  likely  that  E.  M.  F.  in  such  a  cell  is  sufficient  to  pro- 
duce a  current  strength  of  one  or  more  milliamperes.  The 
author  has  tested  fillings  of  this  description  and  found 
that  the  discomfort  complained  of  from  the  electric  current 
produced  by  their  proximity  was  greater  than  that  pro- 
duced by  passing  one  milliampere  of  current  through  the 
fillings  from  a  galvanic  generator.  According  to  Volta's 
Contact  Law,  amalgam  in  this  tiny  cell  is  positively  charged 
and  gold  negatively,  therefore  the  direction  of  flow  of 
current  when  the  circuit  is  closed  is  from  the  amalgam  to 
the  gold  through  the  electrolyte,  and  ions  conveying  electric 
charges  are  electro-positive  from  the  amalgam  to  the  gold 
and  electro-negative  ions  from  the  gold  to  the  amalgam. 
Those  may  consist  of  ions  of  any  salt  present.  There  are 
many  medical  solvents  which  are  neither  electro-positive  nor 
electro-negative,  that  is,  they  do  not  permit  of  separation 
of  ions  because  substances  dissolved  in  them  do  not  under 
ordinary  circumstances  form  any  ions,  even  when  they 
contain  those  salts  which  in  an  electrolyte  are  readily 
dissociated. 


52  ELECTRO-PHYSICS 

Among  these  are  alcohol,  glycerine,  vaseline,  chloroform, 
ether,  and  oils.  These  are  nearly  all  included  in  a  list  given 
by  J.  H.  Morton,1  of  New  York,  of  substances  which  are 
stated  by  him  to  be  acted  upon  or  conveyed  by  electric 
osmosis  or  cataphoresis. 

There  are  many  substances  with  which  we  frequently 
deal  in  electro-therapeutics  that  are  formed  by  the  union 
of  metallic  radicals  with  acid  radicals,  such  compounds 
are  sodium  chloride,  zinc  chloride,  copper  sulphate,  etc., 
which  when  acted  on  by  an  electric  current  separate  into 
electro-positive  and  electro-negative  ions.  The  direction 
of  migration  of  ions  contained  in  a  salt  must  be  known  in 
order  to  determine  the  proper  poles  to  apply  to  medicate 
with  the  ions  desired.  For  example,  if  zinc  ions  are  re- 
quired from  zinc  chloride  and  the  negative  electrode  be 
applied  to  the  site  of  medication,  chlorine  gas  would  be 
liberated  without  any  migration  of  zinc  ions. 

All  acid  radicals  are  negatively  charged  and  all  basic 
radicals  positively.  The  following  are  a  few  electro-chemical 
substances  arranged  under  the  headings  of 


Electro-positive. 

Electro-negative 

Hydrogen. 
Mercury. 
Copper. 
Iron. 

Oxygen. 
Nitrogen. 
Sulphur. 
Chlorine. 

Zinc 

Bromine. 

Sodium. 

Iodine. 

Potassium. 

Arsenic. 

By  the  foregoing  it  is  clear  that  when  a  current  is  passed 
in  a  circuit  through  an  electrolyte  containing  a  salt  in 
solution  the  dissociation  of  the  component  parts  takes 
place,  the  ions  formed  convey  the  electrical  charges  positive 
or  negative  in  opposite  directions  to  the  conducting  elec- 
trodes, where  they  give  up  their  charges.    When  they  have 

1  Cataphoresis,  p.  144. 


ELECTRO-POSITIVE  AND  ELECTRO-NEGATIVE      53 

lost  their  charges  they  reunite  by  the  laws  of  chemistry 
with  the  elements  in  the  electrolyte  for  which  they  have 
affinities.  For  instance,  if  sodium  chloride  is  the  salt  and 
saliva  the  electrolyte  in  the  cell  referred  to  of  amalgam  and 
gold  fillings  between  the  teeth,  when  the  Na  ions  conveying 
their  charges  of  electricity  reach  the  gold  conductor  they 
lose  their  charges  and  the  Na  unites  chemically  with  OH 
(Na+H20.=NaOH+H)  in  the  saliva  to  form  NaOH.  The 
CI  ions  likewise  lose  their  charges  to  the  amalgam  and  the 
CI  unites  chemically  with  the  metal,  tending  to  destroy 
it.  These  chemical  changes  take  place  at  the  electric 
elements  of  all  batteries  or  cells,  and  it  may  reasonably 
be  conjectured  that  this  chemical  change  taking  place  in  the 
instance  of  fillings  of  dissimilar  metals  between  the  teeth, 
may  be  the  cause  of  rapid  disintegration  of  inorganic  salts 
at  the  marginal  edge,  of  the  fillings,  when  this  product  of 
electrolysis  is  an  acid.  Or,  conversely,  may  be  the  means 
of  preserving  the  marginal  edges  in  the  case  of  the  product 
being  an  alkaline  or  antiseptic. 


CHAPTER  III. 
CELLS. 

Leclanche  Dry  Cell — Smee  Cell — Bichromate  of  Potash  Cell — Persul- 
phate of  Mercury  Cell — Bunsen  Cell — Grove  Cell — Daniell  Cell — Second- 
ary Batteries  or  Accumulators — Edison  Storage  Battery — Arrangement 
of  Cells— Cells  in  Series— Cells  in  Parallel— Cells  in  Multiple  Arc- 
Density. 

One  of  the  important  sources  of  supply  of  electric  current 
for  dental  purposes  is  from  cells.  The  principle  of  con- 
struction of  a  voltic  cell  has  been  described  on  page  30.  In 
the  manufacture  of  cells,  makers  observe  strictly  the  laws 
which  govern  the  generation  of  galvanic  currents,  Volta's 
Contact  Law,  resistance,  polarization,  and  depolarization.  A 
constant  and  efficient  supply  of  current  from  a  cell  depends 
on  a  combination  of  adaptability  of  the  plates  to  these  laws, 
the  chemical  action  of  the  electrolyte  employed,  and  the 
difficult  question  of  polarization  and  depolarization. 

Leclanche  Wet  Cell. — Of  the  many  forms  of  primary 
cells  the  one  which  is  most  useful  is  the  Leclanche  cell. 
The  Leclanche  cell  consists  (1)  of  a  glass  jar  in  which  is 
placed  a  porous  pot  containing  in  the  centre  a  carbon  rod 
surrounded  by  coarsely  powdered  carbon  and  peroxide  of 
manganese,  this  forms  the  negative  element;  (2)  a  rod  of 
amalgamated  zinc,  which  forms  the  positive  element;  (3) 
the  electrolyte  consisting  of  a  strong  solution  of  ammo- 
nium chloride  (sal  ammoniac) .  These  constitute  the  internal 
arrangements  of  the  cell.  The  carbon  is  electro-negative 
and  very  dissimilar  to  zinc,  which  is  electro-positive.  The 
electrolyte  ammonium  chloride  (2NH4C1)  acts  chemically  on 
the  zinc  to  form  zinc  chloride  (ZnCl2)  ammonia  (2NH3)  and 
hydrogen  (H2). 

Zn  +  2NH4C1  =  Zn  Cl2  +  2NH3  +  H2 


CELLS 


55 


Fig.  7 


By  the  action  of  the  current  generated  when  the  circuit  is 
closed  (within  the  cell)  the  ion  NH4  migrates  to  the  negative 
element,  and  the  ion  CI  migrates  to  the  positive  element, 
conveying  their  respective  charges  of  electricity  which  they 
unload  to  the  conductor  elements.  The  chlorine  atom 
unites  with  the  zinc  to  form  zinc  chloride;  the  ammonia  is 
soluble  in  water  and  is  dissolved  in  the  electrolyte  solution 
at  the  negative  (carbon),  the  hydrogen  collects  on  the  nega- 
tive element  in  the  form  of  gas  bubbles  and  causes  polariza- 
tion, but  the  carbon  rod  is  surrounded  with  peroxide  of 
manganese  which  is  rich  in  oxygen,  the 
hydrogen  bubbles  unite  with  the  oxy- 
gen to  form  water,  and  by  this  means 
depolarization  is  effected.  When  the 
circuit  is  closed  (that  is,  the  ele- 
ments connected  outside  the  cell  by  a 
conducting  wire)  the  cell  gradually 
weakens,  the  polarization  of  the  cell 
takes  place  faster  than  the  depolariza- 
tion, and  the  flow  of  current  gets 
gradually  less. 

This  kind  of  cell,  however,  has  the 
propert3r  of  recovering  rapidly  when 
the  circuit  is  again  broken,  the  man- 
ganese dioxide  continues  its  action  of 
depolarization  until  the  cell  is  free  from 
the  collection  of  hydrogen  gas  on  the 
negative  element.  The  chemical  action  of  this  cell  ceases  when 
the  circuit  is  broken  so  that  its  elements  are  not  continually 
acted  upon  and  it  is  a  most  lasting  and  economical  cell. 

A  collection  of  these  cells  makes  a  very  useful  battery 
for  dental  purposes,  if  kept  in  a  cabinet  and  the  water  and 
ammonium  chloride  renewed  when  required,  will  remain 
active  for  a  number  of  years,  requiring  very  little  attention. 
The  zincs  are  destroyed  in  time  by  chemical  action  but 
they  are  readily  replaced.  When  it  is  unnecessary  to  move 
the  battery  about,  as  is  the  case  in  a  dental  surgery,  these 
cells  are  admirably  adapted. 


Wet  Leclanche  cell. 


56 


ELECTRO-PHYSICS 


The  electro-motive  force  (E)  of  the  Leclanche  cell  is 
1.47  volts;  there  is  considerable  internal  resistance  (r). 
The  calculation  of  the  current  strength  (c)  can  be  readily 
carried  out  according  to  Ohm's  law.  It  will  be  found  that 
one  cell  is  inadequate  for  dental  purposes  with  the  body  in 
circuit. 

Take,  for  example,  the  resistance  of  1500  ohms  for  the 
body  and  roughly  0.25  ohm  for  internal  resistance.  The 
equation  then  is: 


1.47  V 


R1500  +  0.25r 


0.001  amperes  =  1  milliampere 


Fig.  8 


It  is,  therefore,  necessary  to  collect  the  current  from  a 
number  of  these  cells  by  joining  them  in  series  in  the  form 
of  a  battery. 

Leclanche  Dry  Cell. — This  cell  is  made  on  the  same  prin- 
ciple as  the  wet  cell  described.  Instead  of  the  glass  jar,  the 
case  of  the  cell  is  made  of  zinc  which  is  used  as  the  positive 
element;  in  the  centre  is  the  carbon  nega- 
tive element  surrounded  with  a  layer  of 
manganese  dioxide  as  the  depolarizer. 
The  electrolyte  is  a  pasty  substance  com- 
posed of  some  preparation  of  ammonium 
chloride.  The  cell  is  sealed  at  the  top 
and  is  of  small  size,  the  smallest  measur- 
ing 1|  x  1|  x  3f  inches.  The  current 
produced  by  one  of  these  small  cells  is 
about  equal  to  a  wet  cell  of  ordinary 
size  and  it  will  last  a  fairly  long  time. 
Internal  resistance  of  the  Leclanche  cell 
is  a  factor  in  its  construction  which 
makers  have  devised  several  methods  to 
overcome.  Messrs.  Schall  and  Son  make 
one  form  which  they  supply  in  their 
batteries  in  which  zinc  is  placed  inside  a  cylinder  of  carbon, 
separated  from  it  by  the  electrolyte. 
The  advantages  of  the  Leclanche  dry  cell  over  the  wet 


Leclanche  dry  cell. 


CELLS  57 

are  that  they  are  encased  in  metal  and  are  unbreakable; 
they  contain  no  liquid  which  would  be  liable  to  spill,  they 
are  sealed,  and  there  is  no  corroding  of  the  terminals,  the 
internal  resistance  is  slightly  less  and  E.  M.  F.  slightly 
greater  than  the  ordinary  wet  cell. 

The  principal  disadvantage  they  possess  is  that  they 
cannot  be  recharged,  when  used  up  they  become  worthless, 
but  they  last  long  enough  to  make  this  disadvantage  hardly 
worthy  of  mention.  Two  years  in  constant  use  in  a  dental 
practice  might  well  be  the  life  of  a  dry  cell. 

The  Smee  Cell. — This  is  a  simple  cell  made  of  plates  of 
amalgamated  zinc  to  form  the  positive  element.  These 
are  placed  parallel  to  each  other  and  separated  by  a  plate 
of  silver  coated  with  a  thin  layer  of  platinum  to  form  the 
negative  element.  These  two  metals,  zinc  and  platinum,  are 
far  apart  in  the  contact  series  and  the  electro-motive  force 
generated  is  greater  than  it  would  be  if  the  negative  plates 
were  made  of  either  silver  or  copper,  platinum  being  more 
electro-negative  to  zinc  than  either  silver  or  copper.  The 
electrolyte  consists  of  a  weak  solution  of  sulphuric  acid. 
There  is  no  chemical  depolarizer  in  this  cell,  the  depolariza- 
tion is  mechanical,  that  is,  the  gas  bubbles  are  unable  to 
cling  to  the  surface  of  the  platinum  plate  and  the  plate 
keeps  comparatively  clear  of  this  polarizing  agent,  but  it 
is  an  imperfect  means  of  depolarizing. 

The  zinc  of  the  cell  must  be  withdrawn  when  the  cur- 
rent is  not  being  used  for  the  constant  chemical  action  of 
the  acid  on  the  zinc  destroys  it. 

The  electro-motive  force  of  the  cell  is  about  2  volts  and 
when  in  use  it  is  rapidly  reduced  on  account  of  the  collec- 
tion of  hydrogen  gas  which  collects  on  the  negative  plate. 
This  type  of  cell  has  been  much  used  in  the  past  for 
electro-therapeutic  purposes,  but  for  dental  work  it  has  no 
advantage  over  the  Leclanche  cell. 

Bichromate  of  Potash  Cell. — This  cell  is  constructed  of  a 
plate  of  zinc  which  forms  the  positive  element,  and  two 
plates  of  carbon  set  one  on  either  side  of  the  zinc  which 
form  the  negative  element.     The  electrolyte  is  dilute  sul- 


58 


ELECT  RO-PH  YSICS 


Fig.  9 


phuric  acid.  A  mixture  of  strong  sulphuric  acid,  powdered 
bichromate  of  potash  and  water  is  the  depolarizer.  The 
electrolyte  is  sometimes  varied  by  the  use  of  chromic  acid 
instead  of  potash,  because  its  chemical  action  lessens  the 
internal  resistance.  The  chemical  action  of  the  cell  is  con- 
stant and  the  metal  element  is  arranged  so  that  it  can  be 
removed  from  the  electrolyte  when 
the  cell  is  not  in  use.  It  is  often 
made  in  the  form  of  a  bottle  with 
a  cork  through  which  passes  a  rod 
attached  to  the  zinc,  which  provides 
for  the  lifting  of  the  zinc  clear  of  the 
liquid  when  the  cell  is  not  being 
used. 

By  the  chemical  action  of  the  elec- 
trolyte on  the  plates  when  the  circuit 
is  closed,  a  strong  electric  current  is 
excited,  positively  charged  ions  of 
hydrogen  and  metallic  radicle  pass 
from  the  zinc  to  the  carbon  element, 
at  the  same  time  negatively  charged  ions  of  oxygen  and 
acid  radicle  pass  from  the  carbon  to  the  zinc. 

The  E.  M.  F.  of  the  cell  is  about  2  volts.  It  is  used  when 
a  strong  current  is  required  for  cautery  or  small  incan- 
descent lamp  or  working  an  induction  coil.  With  a  few  of 
these  cells  collected  in  parallel  a  very  strong  current  is  pro- 
duced for  a  short  time  but  polarization  takes  place  rapidly 
within  the  cells  and  internal  resistance  causes  a  rapid  fall  in 
the  current.  It  is  a  useful  form  of  cell,  being  always  ready 
for  use  and  producing  a  strong  current.  Until  recently 
small  batteries  made  of  this  type  of  cell  were  much  used 
for  producing  high  current  strength  for  cautery  and  it  was 
probably  the  most  important  of  the  single  fluid  cells,  but  the 
advent  of  the  accumulator  and  switchboard  has  detracted 
from  this  importance. 

Persulphate   of   Mercury   Cell. — This   is   another   type   of 
single  fluid  cell  from  which  a  high  E.  M.  F.  is  obtained. 
It  is  constructed  of  a  zinc  plate  for  the  positive  element, 


Bichromate  of  potash  cell. 


CELLS  59 

carbon  for  the  negative  element,  and  persulphate  of 
mercury  in  solution  for  the  electrolyte — the  depolarizer 
is  persulphate  of  mercury.  By  chemical  action,  when 
the  circuit  is  closed,  hydrogen  electro-positive  ions  appear 
at  the  carbon  where  they  unload  their  electrical  charges 
to  that  element  and  H  unites  with  the  persulphate  of  mer- 
cury in  the  electrolyte  solution  to  form  sulphuric  acid 
and  deposit  metallic  mercury. 

The  sulphuric  acid  thus  formed  acts  on  the  zinc  element. 
The  chemical  affinity  of  the  hydrogen  for  the  persulphate 
of  mercury  by  which  the  gas  bubbles  are  removed  from  the 
surface  of  the  carbon  constitutes  the  depolarizer. 

The  E.  M.  F.  is  1.5  volts  and  the  internal  resistance  is 
low.  It  is  a  much  used  cell  for  medical  purposes.  Many 
improved  forms  have  been  invented  in  which  the  mercury 
in  the  electrolyte  has  been  utilized  to  amalgamate  the  zinc 
and  by  improvements  in  the  depolarization  of  the  cell  a 
constant  and  lasting  cell  has  been  made. 

The  cells  described  so  far  are  all  single  fluid  cells,  there 
now  remain  to  be  described  briefly  one  or  two  forms  of 
double  fluid  cells;  that  is,  cells  in  which  each  element  is 
surrounded  by  a  different  fluid,  one  of  which  is  the  electro- 
lyte and  the  other  the  depolarizer.  Of  these  the  Bunsen, 
the  Grove,  and  the  Daniell  are  the  best  known. 

The  Bunsen  Cell. — This  consists  of  a  glass  cell  containing 
a  zinc  plate  which  forms  the  positive  element,  a  porous  pot 
containing  a  stick  of  carbon  and  a  strong  solution  of  nitric 
acid  forms  the  negative  element,  the  electrolyte  is  a  dilute 
solution  of  sulphuric  acid  which  is  placed  in  the  cell  about 
the  zinc  and  porous  pot.  The  nitric  acid  is  the  depolarizer. 
By  the  chemical  action  of  the  cell  zinc  is  acted  upon  by  the 
sulphuric  acid  to  form  zinc  sulphurite  and  liberate  hydrogen 
ions  which  migrate  to  the  negative  element  conveying 
positive  charges  of  current,  here  the  current  is  conducted 
away  by  the  carbon,  and  hydrogen  gas  collects  on  the  porous 
pot,  the  depolarizer  (nitric  acid)  combines  with  the  free 
hydrogen  to  form  nitric-peroxide  and  water,  and  depolarizes 
the  cell  by  dispersing  the  gas  bubbles. 


60 


ELECT RO-PE  YSICS 


The  current  strength  from  this  cell  is  greater  than  any 
of  the  single  fluid  cells,  because  of  the  small  resistance 
within  the  cell  by  the  perfect  depolarization;  the  E.  M.  F. 
is  about  2  volts,  and  internal  resistance  only  a  fraction  of 
an  ohm,  and  maximum  current  strength  about  10  amperes. 

The  strong  acid  electrolyte  of  this  cell  soon  destroys  the 
zinc  element  so  that  this  cell  is  not  a  lasting  one.  The 
poisonous  fumes  of  nitrogen  peroxide,  which  are  given  off  in 
the  process  of  oxidization  is  a  great  objection  to  this  form 
of  cell;  it  should  not  be  kept  in  a  room  with  instruments. 

Fig.  10 


Bunsen  cell. 


It  produces  current  for  cautery  loop  or  lamp  and  a  battery 
of  these  cells  can  be  used  to  charge  accumulators  where 
current  from  the  main  is  not  available. 

The  Grove  Cell.— This  cell  has  the  same  construction  as 
the  Bunsen  which  is  a  modification  of  it.  The  negative 
plate  in  the  porous  pot  is  platinum,  but  owing  to  the  cost 
of  this  metal,  carbon  is  substituted  in  the  Bunsen  cell, 
otherwise  the  fluids  and  their  chemical  action  in  the  cell 
are  precisely  the  same. 

The  Daniell  Cell. — This  cell  is  constructed  with  different 
variations  of  the  following  principle.    The  positive  element 


CELLS 


61 


Fig.  11 


is  a  rod  of  zinc  which  is  placed  in  the  centre  of  a  porous 
pot  in  the  centre  of  the  cell,  the  zinc  is  immersed  in  the 
electrolyte  which  is  a  dilute  solution  of  sulphuric  acid  or 
zinc  sulphate.  The  negative  element  is  copper  which 
forms  the  inner  lining  of  the  cell,  the  space  between  it  and 
the  porous  pot  contains  a  saturated  solution  of  sulphate 
of  copper,  with  usually  some  crystals  of  sulphate  of  copper 
to  add  to  the  supply  of  the  salt  in  solution.  The  second 
fluid  is  the  depolarizer  of  the  cell. 

By  the  chemical  action  of  the  H2S04  on  the  zinc,  zinc 
sulphate  (ZnSo4)  and  hydrogen  (H2)  are  formed;  the 
hydrogen  in  passing  from  the  porous  pot  combines  with 
the  copper  sulphate  (CuSo4)  to  form  sul- 
phuric acid  (H2S04)  and  copper  (Cu) .  The 
ITSO4  formed  replenishes  the  supply  of 
electrolyte.  The  copper  ions  unload  their 
charge  of  current  to  the  copper  element 
and  deposit  copper  on  the  lining  of  the 
cell.  There  is  no  polarization  of  the  cell, 
as  the  hydrogen  is  used  up  in  chemical 
combination  with  the  copper  sulphate  and 
the  copper  deposited  on  the  negative  ele- 
ment merely  thickens  the  copper  lining 
of  the  cell. 

By  the  perpetual  change  of  ions  in  this 
form  of  cell  it  remains  active  for  a  long 
time;  the  positive  element  (zinc)  becomes 
destroyed  in  time  but  is  readily  replaced 
and  the  cell  is  then  as  good  as  new.    The  negative  element 
(copper)  will  always  remain  active  because  it  is  being  added 
to  when  the  cell  is  working.     The  electrolyte  is  also  re- 
plenished by  the  formation  of  H2S04  at  the  porous  pot. 

The  E.  M.  F.  of  the  Daniell  cell  is  a  little  over  one  volt 
and  was  originally  taken  as  the  standard  unit  of  electro- 
motive force,  being  sufficiently  near  the  volt  and  being 
nearly  constant,  a  slight  error  was,  however,  subsequently 
discovered  about  this. 

The  internal  resistance  is  practically  nil,  but  placed  at 


Daniell  cell. 


62  ELECTRO-PHYSICS 

an  estimate  of  0.15  ohm   the  current   strength  from  one 
of  these    cells  would  be: 

1  volt 
C  =  0.15  ohms    =  6-6  amP^res- 

Three  of  these  cells  connected  in  parallel  will  produce 
nearly  20  amperes  current  strength. 

The  disadvantage  of  all  acid  fluid  cells  is  that  the  perish- 
able element  should  be  withdrawn  from  contact  with  the 
electrolyte  when  the  current  is  not  required,  this  leaves  the 
cells  open  to  evaporation  of  their  fluid  contents,  and  also 
the  liquid  is  easily  spilled.  They  are  not  as  clean  as  the 
Leclanche  cells  and  require  replenishing  frequently.  The 
refilling,  however,  is  not  a  difficult  matter.  In  places  where 
electrical  supplies  are  not  easily  obtained  the  Daniell  cell 
battery  might  be  useful  to  those  who  have  only  occasional 
use  for  cautery  and  light,  but  their  use  has  been  almost 
completely  superseded  by  the  dynamos  and  secondary 
batteries   (accumulators) . 

Secondary  Batteries  or  Accumulators. — This  type  of  battery 
is  so  constructed  that  when  it  runs  down  it  can  be  again 
charged  by  passing  a  current  through  it.  It  is  made,  in 
one  type,  of  thin  plates  of  lead  moulded  in  the  form  of  a 
grid,  that  is,  holes  punctured  in  the  surface  of  the  plates; 
these  plates  are  placed  close  together  but  carefully  sepa- 
rated by  some  insulator  interposed  at  the  top  and  bottom 
of  the  cell  so  that  they  are  in  no  electrical  contact  except 
through  the  electrolyte,  which  consists  of  a  solution  of 
sulphuric  acid  (about  1  part  to  5  of  water).  The  plates 
which  form  the  positive  pole  are  pasted  with  red  lead, 
that  is,  the  holes  of  the  grid  are  filled  with  the  red  lead; 
and  the  plates  which  form  the  negative  pole  are  filled  with 
sponge  lead,  all  the  plates  of  the  positive  sign  are  connected 
outside  the  cell  by  metal  bringing  them  to  one  terminal, 
and  all  the  plates  of  negative  sign  are  similarly  connected, 
there  being  always  one  more  negative  than  positive  plate, 
and  are  alternately  placed,  a  positive  and  a  negative. 


ACCUMULATORS  63 

There  are  many  variations  in  the  method  of  construction 
of  accumulators  which  it  is  unnecessary  to  enumerate  or 
describe.  This  one  gives  the  principle  of  the  "storage 
battery"  as  it  is  sometimes  called.  The  arrangement 
and  number  of  plates  is  carried  out  with  the  intention  of 
increasing  the  current  with  the  least  amount  of  potential, 
i.  e.,  it  diminishes  the  internal  resistance. 

Four  or  six  cells  connected  in  series  form  a  battery,  each 
cell  of  which  has  a  potential  of  2  volts,  making  a  total 
E.  M.  F.  of  8  or  12  volts  according  to  the  respective 
number  of  cells.  The  capacity  of  the  cells  varies  accord- 
ing to  the  size  of  the  plates  and  the  discharge  of  current  is 
recorded  in  ampere-hours,  i.  e.,  current  can  be  maintained 
at  a  certain  number  of  amperes  for  so  many  hours,  e.  g., 
six  cells  with  a  capacity  of  say  24  amperes  when  charged 
may  be  discharged  either  at  the  rate  of  1  ampere  for  24 
ampere-hours  or  2  amperes  for  12  ampere-hours  or  |  ampere 
for  48  ampere-hours.  When  the  accumulator  is  run  down, 
which  can  be  determined  by  an  ampere-meter  (usually 
called  ammeter)  in  circuit,  it  can  be  recharged  from  the 
opposite  direction  to  that  in  which  it  discharges.  This 
is  done  by  attaching  the  positive  pole  of  the  source  of 
current  for  recharging,  to  the  positive  pole  of  the  battery 
and  the  negative  to  the  negative  of  the  battery.  The 
recharging  of  an  accumulator  battery  may  be  accomplished 
with  current  from  a  number  of  Daniell  or  Bunsen  cells 
connected  in  series,  having  an  E.  M.  F.  of  at  least  10  per 
cent,  higher  than  that  of  the  battery  to  be  charged,  and 
the  current  must  be  allowed  to  pass  for  about  25  per  cent, 
longer  than  the  capacity  of  the  cells,  i.  e.,  a  cell  of  4  ampere- 
hours'  capacity  will  discharge  for  8  hours  at  §  ampere,  but 
must  be  charged  for  10  hours  at  |  ampere. 

If  continuous  main  current  for  lighting  purposes  is  avail- 
able it  is  far  easier  and  cheaper  to  recharge  accumulators 
from  this  source,  provided  the  voltage  of  the  main  approxi- 
mates to  that  of  the  accumulators  or  that  suitable  means 
be  taken  to  reduce  it. 

In   recharging   accumulators   the    capacity    of   the   cells 


64 


ELECT  RO-PH  YSICS 


should  be  taken  into  account  and  the  charging  current 
measured  with  an  ampere-meter  and  calculated  in  ampere- 
hours  to  correspond  with  the  capacity  of  the  cells;  the 
rate  of  charging  should  not  be  too  rapid;  the  most  efficient 
rate  being  usually  marked  by  the  makers,  and  is  usually 
about  one-tenth  the  capacity.  Those  accustomed  to  the 
recharging  of  accumulators  can  determine  when  fully 
charged  by  the  sound  of  effervescence  of  gases  in  the  elec- 
trolyte of  the  cells,  when  they  are  only  partly  charged  slight 
effervescence  is  audible,  and  when  fully  charged  a  distinct 
noise  of  active  effervescence  is  heard  within  the  cells. 


Resistance  lamps. 


In  charging  from  the  main,  the  correct  poles  of  both 
source  of  current  and  battery  must  be  determined,  this 
can  be  carried  out  by  methods  already  described  (p.  42). 
The  like  poles  of  both  are  connected  and  a  resistance,  the 
amount  of  which  is  determined  by  the  current  required, 
is  placed  in  circuit  between  the  negative  pole  of  the  battery 
and  negative  of  the  current  supply.    The  current  is  passed 


ACCUMULATORS  65 

from  the  positive  pole  of  the  main  to  the  positive  terminal 
of  the  accumulators,  through  the  plates  and  electrolyte 
within  the  cells  and  out  at  the  negative  terminal,  and 
through  the  resistance;  carbon-filament  lamps  of  different 
powers  are  often  used  as  a  cheap  and  convenient  form  of 
resistance,   several  usually  being  employed  in  parallel. 

The  accumulator  is  useful  for  heating  a  cautery  loop 
and  for  lighting  mouth  lamps.  It  has  a  very  useful  place 
in  the  surgery,  especially  where  the  current  is  not  available 
from  a  dynamo  source.  The  battery  is  always  ready  for 
immediate  use  as  long  as  it  is  charged:  when  run  down  it 
is  easily  recharged  by  sending  it  to  the  power  house  of  a 
dynamo  machine  or  to  the  makers,  and  it  lasts  for  a  number 
of  years  if  properly  cared  for,  the  acid  kept  at  the  right 
strength,  and  if  not  allowed  to  run  down  completely  before 
it  is  again  charged  or  if  not  badly  charged,  that  is,  charged 
too  quickly  with  too  strong  a  current. 

The  modern  form  of  switch-board  which  is  made  for  use 
where  dynamo  current  is  available  has  quite  superseded 
the  secondary  battery.  It  is  certainly  far  more  convenient 
for  many  purposes,  which,  until  its  introduction,  the  storage 
battery  was  the  only  available  means  of  procuring  current 
in  that  form — but  the  accumulator  will  always  find  a  use- 
ful place  in  the  surgery  of  dentists  situated  in  places  where 
the  street  current  is  not  available  or  not  installed,  or  where 
it  is  alternating  and  the  current  required  is  a  continuous 
current,  or  where  a  portable  battery  is  required. 

The  ordinary  dental  motor  engine  can  be  run  by  a  col- 
lection of  accumulator  cells  arranged  in  series,  6  cells  will 
produce  an  E.  M.  F.  of  12  volts,  which  is  ample  to  run  the 
dental  engine  indefinitely  by  keeping  the  cells  charged. 

The  Edison  Storage  Battery. — This  form  of  accumulator 
is  one  of  the  latest  inventions  of  Mr.  Thomas  A.  Edison, 
which  bids  fair  to  revolutionize  the  storing  of  electric 
current  for  many  purposes,  certainly  for  dental  purposes 
there  is  no  method  more  suitable.  It  does  away  with  the 
lead  and  acid  so  objectionable  in  the  lead  plate  form  of 
storage  cells,   eliminates  the   element  of  care  and  knowl- 


66 


ELECTRO-PHYSICS 


edge  necessary  in  the  working  of  the  lead  cells,  while  the 
life  of  the  cells  is  increased  many  fold;  reduced  size  and 
weight  with  the  same  storage  capacity  are  improvements 
of  great  value.  The  cells  are  made  in  various  sizes  and 
numbered  by  the  makers  according  to  their  capacity,  the 
ampere-hour  output  depending  on  the  number  and   size 

Fig.  13 


Positive  and  negative  plates,  A.4  type. 


of  the  plates,  but  the  voltage  is  the  same,  viz.,  1.2  volts  per 
cell.  The  voltage  it  will  be  observed  is  less  than  that  of 
the  lead  cells.  Each  cell  of  A.4  type  (which  is  the  size 
which  would  make  a  useful  battery  for  working  a  dental 
engine)  contains  four  positive  and  five  negative  plates. 
"The    negative    plate    is    comprised    of    twenty-four    rec- 


ACCUMULATORS 


67 


Fig.  14 


tangular  pockets  supported  in  three  horizontal  rows  in  a 
nickel-plated  grid,  each  pocket  being  \  inch  wide  and  3 
inches  long.  The  pockets  are  made  of  thin  nickel-plated 
steel,  perforated  with  fine  holes.  Each  pocket,  after  being 
filled  with  iron  oxide,  is  subjected  to  high  pressure,  so  that 
it  becomes  practically  integral  with  the  supporting  grid. 

"The  positive  plate  consists  of  two 
rows  of  round  rods  or  pencils,  30  in 
number,  held  in  vertical  position  by 
a  steel  supporting  frame.  The  per- 
forated tubes  into  which  the  nickel 
active  material  is  loaded  are  made  of 
nickel-plated  steel.  These  tubes  are 
put  together  with  eight  steel  rings." 

The  plates  consist  of  iron  oxide  for 
the  negative  and  nickel  hydrate  for 
the  positive  plate  acted  on  by  a  solu- 
tion of  caustic  potash  in  pure  water, 
which  is  the  electrolyte.  The  cells 
are  assembled  in  the  usual  manner,  a 
positive  and  a  negative  plate  alter- 
nately, there  being  always  one  more 
negative  plate  than  positive.  The 
plates  of  each  sign  are  connected  to 
a  nickel-steel  rod  and  kept  the  proper 
distance  apart  by  washers  and  nuts 
which  hold  them  firmly  in  position. 
Altogether  the  cells  when  complete 
are  of  most  substantial  mechanism 
with  nothing  to  go  wrong  with 
them,  no  buckling  of  plates,  no  fear 
doing  damage,  for  the  battery  may 
and  discharged  at  once  without  injury  to  the  plates.  The 
battery  is  kept  in  order  by  simply  replenishing  with  pure 
water  when  necessary,  and  charging  and  discharging  may 
be  done  almost  indefinitely  without  fear  of  the  plates 
being  used  up,  as  in  the  case  with  the  ordinary  lead  plate 
cells. 


Assembled  positive  and 
negative  plates. 

of   short-circuiting 
be    short-circuited 


ELECTRO-PHYSICS 


The  cells  to  form  a  battery  are  connected  in  series,  five 
cells  of  the  type  described  will  work  a  dental  engine  of  6 
volts  winding  for  a  very  long  time,  revolving  at  a  speed  of 
from  1000  to  3000  revolutions  per  minute.  There  are  no 
fumes  from  the  electrolyte,  so  that  the  battery  may  be 
placed  in  a  neat  hardwood  case  and  kept  in  the  surgery 
in  close  proximity  to  the  engine. 

Arrangement  of  Cells. — The  E.  M.  F.  of  cells  has  been 
shown  to  depend  on  the  dissimilarity  of  the  plates,  the 
conductivity  of  the  electrolyte,  the  area  and  proximity  of 
the  plates  and  the  internal  resistance  set  up  by  polarization 
within  the  cell,  the  size  of  the  cell  has  no  effect  on  the 
E.  M.  F.  of  the  cell,  a  small  Leclanche  cell  will  have  almost 
the  same  potential  as  a  large  one;  with  the  increase  of 
size  (as  long  as  the  plates  are  of  the  same  nature)  the  in- 
ternal resistance  (r)  is  increased,  so  that  the  output  of 
current  strength  is  about  the  same. 

Fig.   15 


Cells  in  series. 

Cells  in  Series. — The  E.  M.  F.  of  one  Leclanche  cell 
is  about  1.47  volts,  which  when  resistance  is  taken  into 
account  produces  a  current  strength  quite  inadequate  for 
therapeutic  purposes,  but  this  form  of  cell  has  been  shown 
to  be  one  of  the  most  useful  for  producing  current  for  dental 
ionic-medication;  in  order,  therefore,  to  increase  the  current 
strength  a  number  of  cells  are  connected  in  series,  that  is, 
the  zinc  of  the  first  cell  is  connected  with  the  carbon  of 
the  second  and  so  on  till  all  are  connected,  that  will  leave 
the  terminal  carbon  at  one  end  free  and  the  last  zinc  at 
the  other  end  free. 


ARRANGEMENT  OF  CELLS  69 

The  potential  of  the  cell  is  from  the  zinc  to  the  carbon 
within  the  cell,  therefore  at  the  terminal  the  flow  of  current 
is  +  at  the  carbon  and  —  at  the  zinc. 

According  to  Ohm's  law,  if  each  of  these  cells  has  an 
E.  M.  F.  of  1.47  volts  by  collecting  6  of  them  in  series 
the  E.  M.  F.  is  increased  to  nearly  9  volts. 

1.47  volts  X  6  =  8.82  volts 

and  three  times  that  number  of  cells  connected  in  the 
same  way  will  give  about 

1.47  volts  X  6X  3   =  26.42  volts. 

The  voltage  of  a  cell  or  collection  of  cells  is  simply  the 
electro-motive  force.  What  most  concerns  us  is  the  current 
strength  which  these  cells  will  produce,  and  to  find  this 
the  internal  resistance  of  the  cells  and  external  resistance 
of  the  circuit  must  be  calculated.  The  resistance  of  a 
Leclanche  cell  varies.  When  the  circuit  is  first  closed  it  is 
stronger  than  after  it  has  been  closed  for  some  time  because, 
as  we  have  seen,  polarization  takes  place  faster  than  de- 
polarization, but  say  it  is  on  an  average  2  ohms  and  the 
external  resistance  of  the  circuit  1  ohm,  the  current  strength 
(c)  of  one  Leclanche  cell  would  be^  worked  out  by  Ohm's 
law. 

1.47  volts        1.47 
C  =    -d-i     i     o"  =  ~ <T   ~~  °'49  amP^re  =  490  ma. 

Now  if  we  take  18  cells  in  series  and  consider  the  resistance 
(R)  and  internal  resistance  (r)  we  shall  find  that  the  re- 
sistance has  a  very  marked  effect  on  the  current  strength, 
for  instead  of  the  current  strength  being  18  times  as  great 
it  is  only  raised  not  quite  twice  as  much,  thus 

1.47  volts  X  18  cells  26.42  volts 

C  =  — ^z — ,    ,  _   .,  10. —    =  : — r-^ — r —    =  0.714  amp.   =  714  ma. 
Rl  +  (r2  X  18)  1  +  36  ohms 

It  may  be  taken  that  this  output  of  714  ma.  current 
strength  is  fairly  accurate  as  far  as  18  Leclanche  cells  are 


70  ELECTRO-PHYSICS 

concerned;  this  is  about  the  number  of  these  ceils  which 
will  constitute  a  useful  battery  for  ionic  medication  for 
all  dental  purposes,  the  full  current  obtainable  from  such 
a  battery  will  of  course  be  more  powerful  than  it  is  possible 
to  use  in  the  mouth  of  a  patient,  but  the  current  weakens 
after  the  battery  has  been  in  use  for  a  time  and  it  is  best 
to  have  a  reserve  of  current  strength;  it  is  essential  to  have 
it  controlled  by  a  finely  graded  rheostat  in  circuit,  through 
which  the  current  must  pass  before  reaching  the  patient. 
The  resistance  of  the  body  must  now  be  taken  into  con- 
sideration. If  a  milliampere  meter  be  connected  in  circuit 
with  the  current  flowing  from  the  terminal  of  the  battery, 
when  the  circuit  is  closed  without  the  resistance  of  the 
body  in  circuit  but  with  nearly  all  the  resistance  of  the 
rheostat  in  use,  the  milliampere  meter  needle  will  be  violently 
deflected  5  or  10  milliamperes,  the  resistance  of  the  wire 
leads  being  only  one  or  two  ohms;  but  a  very  different 
result  will  be  observed  if  the  resistance  of  a  patient  be 
placed  in  the  circuit.  Take  for  instance  a  patient  having 
a  resistance  of  2000  ohms,  a  considerable  amount  of  current 
will  be  required  from  the  battery  to  register  two  or  three 
ma.  on  the  milliampere  meter  dial.     According  to  Ohm's 

1.47  volts  X  18  cells  26.42  volts 

C  =    R2000  +  (r2  X  18)     =  2000  +  36  ohms  =  °-012  amp"  =  12  ma< 

law  12  ma.  will  then  be  the  greatest  amount  of  current 
strength  which  will  be  available  from  a  battery  of  18  cells 
with  the  resistance  of  a  patient  of  2000  ohms  in  series.  This, 
as  has  been  said,  must  be  controlled  by  a  rheostat  which 
is  really  resistance  placed  between  the  battery  and  the 
patient  to  regulate  the  output  of  current  strength,  so  that 
instead  of  the  full  12  ma.  passing,  only  one  or  two  ma.  pass 
according  to  the  requirements. 

To  summarize,  it  has  been  shown  that  18  Leclanche  cells 
connected  in  series  produce  electro-motive  force  of  about 
26  volts  and  a  maximum  current  strength  of  about  714  ma. 
That  with  the  resistance  of  the  body  of  2000  ohms  in  series 


ARRANGEMENT  OF  CELLS 


71 


the  maximum  current  strength  is  about  12  ma.  That  the 
maximum  current  strength  of  one  cell  is  about  490  ma. 
which  is  only  slightly  increased  to  714  ma.  by  connecting 
18  cells  in  series,  showing  that  the  E.  M.  F.  is  added  to- 
gether while  the  r  remains  almost  the  same.  The  cur- 
rent which  one  cell  will  force  through  a  large  resistance 
will  be  much  less  than  the  amount  which  18  cells  will 
force  through  a  similar  resistance,  although  without  any 
external  resistance  the  C  is  about  the  same,  hence  the 
necessity  for  a  number  of  cells  in  a  battery  which  is  in- 
tended for  use  with  the  body  as  resistance;  the  pressure, 
potential  or  E.  M.  F.  must  be  of  proportions  great  enough 
to  overcome  the  resistance  met  in  circuit. 

Fig.  16 


Cells  in  parallel. 


Cells  in  Parallel. — To  connect  cells  in  parallel  all  the 
terminals  of  one  sign  are  connected  together  with  one  wire 
to  form  one  pole  of  the  battery  and  all  the  other  terminals 
are  connected  to  form  the  other  pole,  by  this  arrangement 
the  collection  of  cells  act  like  one  cell,  the  internal  resist- 
ance, however,  is  considerably  reduced,  so  that  a  greater 
maximum  current  is  obtainable.  This  arrangement  is 
therefore  only  of  use  when  the  resistance  of  the  external 
circuit  is  very  low  (and  its  chief  use  in  medical  and  dental 
work  is  for  heating  cauteries  where  low  E.  M.  F.  and  a 
high  current  is  required). 

Cells  are  connected  in  parallel  when  a  large  current 
strength  is  required  such  as  for  cautery.  To  get  the  greatest 
amount  of  current  strength  the  choice  of  cells  should  be 


72  ELECTRO-PHYSICS 

those  with  the  least  internal  resistance,  so  that  for  this 
purpose  Leclanche  cells  are  least  serviceable.  The  bichro- 
mate cells  and  Grove's  cells  are  useful  because  the  E.  M.  F. 
of  these  cells  is  greater,  owing  to  the  nature  of  the  electro- 
lyte, the  proximity  of  the  plates,  and  the  area  of  the  plates. 
The  E.  M.  F.  of  a  bichromate  cell  is  about  2  volts  with 
an  internal  resistance  of  about  1  ohm,  one  of  these  cells 
will  produce  considerable  current  strength  for  cautery  or 
light,  but  if  six  are  arranged  in  parallel  the  current  strength 
is  materially  increased.  If  we  add  two  ohms  for  the  ex- 
ternal resistance  of  the  cautery  wires,  according  to  Ohm's 
law  the  current  strength  can  be  calculated: 

2  volts  X  6  cells        12 
C  = R2    .     i =  2i  =  5-5  amperes. 

If  one  such  cell  be  tried  we  should  have  a  current  by  the 
same  calculation: 

2  volts  2 


C  = 


R2  +  1  ohm  =  3  =  °-6  amp^eS 


which  would  be  insufficient  to  heat  a  cautery  loop  or  light 
a  small  lamp. 

Thus  it  is  seen  that  by  adding  cells  in  parallel  the  E.  M.  F. 
remains  practically  the  same  as  one  cell  but  the  current 
strength  is  greatly  increased. 

Accumulators  for  cautery  work  are  better  than  voltic 
cells,  their  internal  resistance  being  very  low. 

Cells  in  Multiple  Arc. — This  is  another  method  of 
connecting  cells  which  has  the  effect  of  reducing  the  in- 
ternal resistance  and  increasing  the  current  strength. 
One  way  of  arranging  cells  by  this  method  is  as  follows: 
take  six  cells  and  connect  three  together  in  series,  and  the 
other  three  also  in  series,  then  join  the  positive  pole  of 
each  collection  of  three  to  form  one  pole,  and  the  negative 
pole  of  each  to  form  the  other  pole;  the  effect  of  this  com- 
pound connection  will  be  to  double  the  size  of  the  cells  and 
to  halve  their  number.     This  can  be  shown  by  calculating 


ARRANGEMENT  OF  CELLS— DENSITY  73 

as  before  (take  for  example  the  bichromate  cell  with  E.  M.  F. 
of  2  volts  and  internal  resistance  of  1  ohm  and  say  the 
external  resistance  is  0.5  ohm).  The  E.  M.  F.  would  be 
that  of  three  cells  (3X2  =(3  volts);  the  internal  resistance 
would  be  that  of  three  cells  of  double  the  size  (1  ohm  X  3-^2 
=  1.5);  therefore 

E  6  6X2  12 

X  „     ,    .   „  a   =  n     ,    nC   ss  a   =  7>    =  1-3  ampfcres. 


^""R  +  r^R+rXB        1+0.5   X  6 

Another  variation  of  the  compound  connection  of  cells 
consists  in  collecting  each  group,  say  3  cells  in  parallel  and 
then  these  two  groups  in  series.  This  will  also  reduce  the 
internal  resistance  and  therefore  produce  a  greater  current 
strength. 

The  arrangement,  of  galvanic  cells  in  series  and  in  parallel 
have  a  useful  place  in  electro-therapeutics,  especially  where 
it  is  necessary  to  take  about  instruments  to  work  away 
from  the  surgery  or  where  an  alternating  current  circuit  is 
supplied  by  the  mains;  but  in  dental  practice  where  nearly 
all  work  is  done  in  the  surgery,  batteries  are  nearly  entirely 
superseded  by  the  use  of  current  from  the  main,  where 
this  is  continuous,  which  can  be  controlled  and  regulated 
by  switchboards  from  which  the  current  can  be  obtained 
in  every  conceivable  form  for  every  requirement.  Alter- 
nating current  mains  can  be  used  but  they  necessitate  a 
motor-dynamo  to  convert  the  current  into  continuous. 

The  battery  of  cells  in  series,  however,  is  preferred  by 
many  who  use  a  continuous  current  for  ionization  and 
cataphoresis,  and  the  advantage  undoubtedly  is  that  it  is 
impossible  to  obtain  a  severe  shock  from  it. 

Density. — We  have  seen  that  the  distribution  of  the 
current  on  a  charged  conductor  is  on  its  surface,  and  that 
if  the  surface  is  spherical  the  distribution  is  all  over  that 
surface  evenly,  but  if  it  be  pointed  the  density  is  greatest 
at  the  point.  So,  too,  if  it  be  knife-edged  the  edges  will 
display  greater  density,  whereas  the  flat  surfaces  are  less 
charged.  These  facts  have  an  important  bearing  on  the  prac- 


74  ELECTRO-PHYSICS 

tical  use  of  the  current.  In  the  construction  of  electrodes, 
the  purpose  for  which  they  are  required  and  the  manner 
in  which  they  are  to  be  applied  are  considerations  which 
should  be  carefully  thought  out  with  regard  to  the  density 
of  the  current  likely  to  be  produced  by  the  shape,  size, 
and  diameter  of  the  conductor.  If  it  is  required  to  pass 
current  of  25  ma.  into  the  body,  a  flat  electrode  of  5  cm. 
diameter  would  be  twice  as  painful  to  the  patient  as  one 
10  cm.  in  diameter,  because  the  density  in  5  cm.  area 
would  be  so  much  greater.  So,  too,  a  fine  pointed  con- 
ductor will  intensify  the  current  at  the  point,  which  will 
be  painful  even  with  a  current  strength  of  2  ma.,  whereas 
a  conductor  which  is  round  and  5  mm.  in  diameter 
would  not  be  felt  at  all  with  the  same  current  strength. 
Also  a  flat,  knife-like  conductor  will  intensify  the  current 
at  the  edges  while  the  flat  surfaces  will  have  a  less  density, 
but  if  the  cross-section  be  increased  and  the  edges  rounded 
the  density  will  be  diminished,  being  more  evenly  dis- 
turbed over  the  whole  surface. 

Taking  these  points  into  consideration  it  becomes  pos- 
sible to  use  more  current,  say,  for  instance,  in  a  pyorrhoea 
pocket  without  discomfort  to  the  patient,  or  on  the  other 
hand,  to  produce  perfect  sterilization  in  the  root  of  a  dead 
tooth  by  introducing  a  very  fine  pointed  conductor,  a 
dead  tooth  having  little  sensation  except  the  conductor 
reaches  the  apex.  Density  then  has  to  be  considered  for 
the  comfort  of  the  patient  in  the  efficient  use  of  the  current 
especially  in  mucous  or  periodontal  membrane;  one  of 
the  important  factors  in  ionic  medication  is:  the  greater 
the  current  strength  that  is  possible  to  be  used  without 
pain,  the  more  penetrating  will  the  medication  be,  and 
in  order  to  obtain  this  it  is  necessary  carefully  to  consider 
the  area  and  shape  of  the  electrode  which  is  to  convey  the 
current  to  the  parts.  It  is  often  difficult  to  get  an  electrode 
large  enough  to  diminish  the  density  sufficiently  to  cause 
no  discomfort  when  4  or  5  ma.  is  the  current  strength  for 
ionization  of  affections  about  the  roots  of  live  teeth  or  the 
gingival  margin. 


CHAPTER  IV. 

MAGNETIC  FIELD,  DYNAMO  CURRENTS,  AND 
BATTERIES. 

Inducted  Currents — Self-induction — Induction  Coil — Secondary  Coil — 
Continuous  Current  —  Alternating  Current  —  Transformers  —  Batteries  — 
Home-made  Battery  —  Switchboard  for  Voltic  Cell  Battery  —  Cautery 
Battery — Accumulator  Battery — Induction  Coil  Battery. 

When  a  magnet  is  brought  in  close  proximity  to  iron 
filings  it  attracts  the  filings  and  they  cling  to  its  surface. 
If  the  filings  are  placed  on  paper  and  the  magnet  placed 
under  the  paper  and  the  paper  slightly  tapped  the  filings 
will  be  observed  to  arrange  themselves  in  definite  lines  and 
curves.  This  indicates  that  for  some  distance  around  the 
magnetized  iron  there  is  a  space  or  field  which  is  permeated 
with  the  influence  or  force  of  the  magnetism;  this  field  is 
termed  the  magnetic  field.  It  exists  about  all  magnets 
and  experiments  have  been  made  to  prove  that  the  force 
created  in  this  field  takes  certain  lines  and  curves.  In  a 
bar  magnet  for  instance,  the  one  end  is  north  pole  and 
the  other  south  pole;  if  it  is  balanced  on  a  pivot  in  the 
centre,  which  is  the  equator  or  neutral  zone  of  the  magnet, 
the  north  pole  will  swing  to  the  north  as  any  ordinary 
pocket  compass  does.  From  the  ends  of  the  magnet  the 
magnetic  force  radiates  in  curves  in  the  direction  from 
one  pole  to  the  other,  there  being  a  considerable  space 
about  the  magnet  which  is  the  magnetic  field.  The  strength 
of  the  force  in  a  bar  magnet  is  greater  at  each  end.  In 
a  curved  magnet,  on  the  other  hand,  the  greatest  force  is 
exerted  between  the  two  poles  from  their  nearest  points. 

This  magnetic  force  which  permeates  the  field  about 
the  magnet  is  conducted  by  the  air,  but  air  has  been  found 


76 


ELECTRO-PHYSICS 


to  be  a  poor  conductor  of  magnetism,  whereas  iron  is  a  good 
conductor  and  if  the  magnet  is  strong  enough  iron  brought 
in  contact  with  it  will  itself  become  magnetized  to  some 
degree. 

Fig.   17 


>;X>:;i^:><\ 

\\\\ 

•  ''  ■'  /  .' 

~~~---;i 

N    < 

Magnetic     axes 

'-■:'-■'' 

.-"."-:' 

*                                              \v\w 

?;•--, 

■5-- 


Lines  of  force  of  magnetic  field. 


Fig.  18 


Electro-magnet. 


A  temporary  magnet  is  made  by  winding  insulated 
copper  wire  around  an  ordinary  piece  of  soft  iron  bent 
in  the  shape  of  a  horseshoe  and  by  passing  an  electric 
current  through  the  wire.  As  the  wire  does  not  touch  the 
iron  it  is  evident  that  the  magnetism  which  is  imparted 
to  the  iron  is  obtained  from  a  magnetic  field  about  the 
current  conducting  wire.  This  magnetic  field  exists  around 
all  wire  conducting  electric  current  and  the  force  of  the 
field  is  intensified  by  the  curving  of  the  wire  (making  a 


MAGNETIC  FIELD  77 

spiral  of  it,  as  by  winding  stiff  copper  wire  around  a  lead 
pencil  and  removing  the  pencil),  and  also  by  the  intensity 
of  the  current  passed  through  the  wire;  the  field  is  also 
stronger  when  the  iron  is  placed  in  it. 

A  magnet  made  by  passing  current  through  wire  en- 
circling a  piece  of  soft  iron  is  only  magnetic  so  long  as  the 
current  is  passing,  it  is  a  temporary  magnet. 

Sir  Oliver  Lodge  points  out  that  the  magnetic  field 
about  a  current  conducting  wire  exerts  force  in  the  field 
exactly  similar  to  force  about  a  magnet  and  he  describes 
it  as  electricity  in  rotations;  many  experiments  have  been 
performed  with  the  ordinary  compass-like  magnet  in  a 
magnetic  field  to  show  the  rotatory  action  of  the  current 
in  a  magnetic  field.  If  a  magnetic  compass  be  suspended 
in  the  air  it  will  point  north  and  south,  but  if  a  wire  con- 
veying current  from  any  electrical  source  be  brought  par- 
allel above  the  compass  so  that  it  also  runs  north  and 
south  with  the  positive  and  negative  running  from  the 
south  to  the  north,  when  the  wire  approaches  the  compass 
near  enough  to  bring  it  into  the  magnetic  field,  the  X-point 
of  the  compass  will  deflect  to  the  west,  showing  that  the 
force  of  the  field  is  outward  and  backward,  rotatory,  in 
the  same  direction  as  the  lines  described  about  an  ordinary 
magnet.  On  this  principle  of  the  force  of  the  magnetic  field, 
galvanometers  are  constructed  to  measure  the  force  of 
current  strength. 

The  energy  derived  from  the  field  of  force  about  an 
insulated  conductor  of  current  by  which  temporary  mag- 
nets are  created  is  termed  electro-magnet,  and  as  the  mag- 
netism so  derived  ceases  as  soon  as  the  current  ceases,  the 
principle  is  applied  in  the  construction  of  many  electrical 
apparatuses  in  which  rise  and  sudden  fall  of  energy  operates 
in  mechanical  devices. 

An  electro-magnet  has  been  devised  for  use  with  the 
ordinary  street  current  with  a  lamp  in  circuit  as  a  reducer 
of  the  current,  which  when  applied  to  the  cavity  of  a  tooth 
or  near  the  surface  of  a  root-canal  in  which  is  a  broken 
drill  or  any  piece  of  steel,  if  the  metal  is  loose  will  extract 


78  ELECTRO-PHYSICS 

it  with  ease  by  the  powerful  electro-magnetic  force.  Mag- 
netic force  is  not  conducted  in  the  same  way  that  current 
is  so  that  the  energy  is  not  felt  by  a  patient.  Electro- 
magnets have  been  constructed  of  enormous  power,  capable 
of  raising  tons  of  metal.  The  strength  of  electro-magnetic 
field  depends  on  the  current  strength  which  is  used  in 
creating  it. 

Induced  Currents. — From  the  foregoing  it  has  been  shown 
that  there  is  a  field  of  magnetic  force  about  all  wire  con- 
ducting current.  Faraday  discovered  that  if  another  wire 
was  brought  within  the  influence  of  this  field,  it  had  the 
power  of  inducing  current  at  the  moment  of  turning  on 
and  turning  off  the  current  (that  is,  at  the  make  and  break 
of  circuit) ;  also  if  the  current  strength  be  varied  or  changed 
in  direction.  The  current  so  produced  in  the  adjoining 
wire  is  momentary  and  occurs  at  the  make  or  break  or 
change  of  potential.  Also,  the  direction  of  the  induced 
current  varies  with  the  make  and  break  of  the  circuit  in 
the  primary  or  current  conducting  wire;  when  the  current 
is  turned  on  in  the  first  wire  the  momentary  induced  cur- 
rent in  the  second  wire  flows  in  the  opposite  direction,  and 
when  the  current  is  turned  off  the  current  is  again  induced 
in  the  second  but  in  the  same  direction  as  the  primary 
wire.  The  same  phenomenon  of  induction  takes  place 
when  the  current  is  increased  in  the  primary  wire,  the 
induced  current  flows  in  the  secondary  wire  in  the  opposite 
direction,  but  when  it  is  reduced  in  strength  the  induced 
current  flows  in  the  same  direction  as  the  primary  wire. 
This  induction  of  current  in  a  magnetic  field  about  a  wire 
conducting  current  is  due  to  the  expansion  and  contraction 
of  the  magnetic  field  of  force.  The  above  is  the  simplest 
form  of  induction  that  can  be  imagined  and  may  be  prac- 
tically illustrated  in  the  adjoining  sketches  of  two  parallel 
wires,  the  one  conveying  current  and  the  other  inducting 
current,  the  arrows  showing  the  direction  of  the  induced 
current  at  the  moment  of  make  or  break  of  circuit. 

While  the  current  is  flowing  uniformly  in  the  primary 
circuit  no  induced  current  is  formed;  it  is  only  at  the  in- 


INDUCED  CURRENTS  79 

stant  of  make  and  break  or  increase  and  decrease  of  potential 
that  induction  takes  place. 

Fig.  19 


A,  primary  current  at  make;  B,  induced  current  at  make. 

The  magnetic  force  in  the  field  about  an  electric  wire 
is  in  the  direction  at  right  angles  to  the  direction  of  flow 

Fig.  20 
-< < 


A,  direction  of  current  before  break;  B,  induced  current  at  break. 

of  current  in  the  wire,  precisely  in  the  same  manner  as  the 
field  about  a  magnet,  forming,  as  it  were,  concentric  circles 


80 


ELECT  RO-PH  YSICS 


about  the  wire;  when  the  wire  is  bent  in  the  shape  of  a 
coil  the  magnetic  field  of  force  is  increased,  but  the  re- 


Fig.  21 


Field  of  force  about  a  wire. 


sistance  is  also  increased,  so  the  strength  of  the  magnetic 
field  will  depend  on  the  strength  of  the  current  and  will  be 


Fig.  22 


Field  of  force  in  a  coil. 

proportional  to  the  current  and  the  field  of  force.  The 
introduction  of  an  iron  core  will  also,  as  has  been  shown, 
increase  the  strength  of  the  field. 


SELF-INDUCTION  81 

If  a  secondary  coil  be  introduced  into  the  magnetic 
field  of  a  stationary  primary  coil  and  be  moved  away  or 
toward  it,  current  is  exerted  in  the  secondary  coil;  this 
effect  is  produced  by  the  magnetic  circles  of  force  about 
the  active  coil  being  cut  into  by  the  circles  of  force  in  the 
induced  current  of  the  other  coil.  This  principle  of  in- 
duction is  carried  out  in  the  production  of  current  by 
dynamos  in  which  armatures  are  constructed  to  cut  the 
lines  of  force  from  the  field  magnets  by  their  motion. 

Self-induction. — This  takes  place  in  a  simple  coil  or 
primary  wire  and  is  the  effect  of  passing  a  current  through 
a  coil  by  which  a  magnetic  field  is  set  up  about  the  con- 
ducting wire  of  the  coil  and  a  reaction  of  E.  M.  F.  is  set 
up  in  the  conducting  wire  itself  at  the  make  and  break  of 
the  circuit;  at  the  make  of  the  circuit  the  current  is  resisted 
by  the  induced  current  in  the  magnetic  field  in  an  opposite 
direction,  and  at  break  of  the  circuit  the  induced  current 
is  momentarily  conducted  by  the  conducting  coil  in  the 
same  direction  as  the  current  in  circuit.  In  other  words, 
each  coil  induces  a  current  in  the  next.  If  a  current  from 
a  battery  be  passed  through  a  single  coil  and  the  terminals 
be  so  arranged  that  there  will  be  a  small  gap  over  which 
a  spark  can  pass,  on  breaking  the  circuit  a  spark  will 
be  observed  at  the  spark  gap  of  a  size  large  enough  to 
ignite  an  ordinary  gas  jet.  The  current  which  produces 
this  spark  is  the  self-induced  current  in  the  coil.  If  the 
wires  from  the  same  battery  do  not  include  a  coil  in  circuit, 
the  breaking  of  the  current  with  a  similar  spark-gap  will 
produce  no  visible  spark.  The  strength  of  the  self-induced 
current  is  greatly  magnified  when  the  magnetic  field  about 
the  coil  is  increased,  as  when  the  current  is  supplied  from 
an  alternating  dynamo  and  still  further  increased  when  an 
iron  core  be  introduced  into  the  centre  of  the  coil  on  the 
principle  of  an  induction  coil.  The  extra  resistance  intro- 
duced into  the  coil  by  the  strong  magnetic  field  produced 
by  the  alternating  current  or  the  magnetism  about  the  iron 
core,  reinforces  the  self-induced  current  and  on  breaking 
the  current  a  large  spark  is  produced  according  to  the 
6 


82  ELECTRO-PHYSICS 

strength  of  the  current  employed;  moreover,  the  strength 
of  the  self-induced  current  will  be  increased  or  diminished 
by  the  number  of  turns  in  the  coil,  the  larger  the  number 
of  turns  in  the  coil  the  greater  will  be  the  magnetic  field, 
and  the  stronger  the  self -induced  current. 

The  resistance  set  up  in  such  a  coil  by  the  self-induction 
current  is  very  much  greater  than  the  ordinary  resistance 
of  the  same  wire  not  formed  into  a  Solenoid,  as  the  hollow 
spiral  of  a  self-induction  coil  is  termed;  the  resistance 
only  occurs  when  the  current  begins  to  flow  or  increases 
its  strength,  a  steady  current  meets  with  no  resistance 
from  self-induction. 

The  Induction  Coil. — This  is  probably  one  of  the  commonest 
and  best  known  electrical  devices  in  use  for  medical  pur- 
poses. So  far  it  has  been  little  used  in  dental  treatment 
and  it  is  hard  to  conceive  many  uses  to  which  it  can  be 
directly  applied.  The  principle  of  the  induction  coil  should, 
however,  be  studied  for  it  enters  into  the  construction  of 
numerous  electrical  devices,  which  are  of  importance  to 
dental  science  and  has  a  direct  bearing  on  them,  such  as 
the  a>ray  and  high-frequency  coils.  It  consists  of  a  primary 
coil,  a  secondary  coil,  an  interrupter,  with  sometimes  a 
condensor. 

A  simple  form  of  coil  consists  of  a  core  of  iron  or  bundles 
of  iron  wire  around  which  is  wound  the  primary  coil  con- 
sisting of  a  number  of  turns  of  wire  which  is  insulated 
with  silk  wound  around  it.  The  core  must  be  carefully 
insulated  from  the  primary  coil.  The  coil  is  connected 
with  a  battery  and  conveys  the  primary  current.  The 
interrupter  is  placed  opposite  the  core  and  is  a  vibrating 
spring  with  a  metallic  head  which  affords  the  spring  mo- 
mentum when  set  in  motion.  A  stationary  adjustable 
screw  with  a  platinum  point  is  fixed  at  the  middle  of  the 
spring.  The  spring  and  primary  coil  are  connected  to  one 
pole  of  the  battery  and  the  adjustable  screw  is  connected 
to  the  other  pole.  When  the  current  is  passed  through  the 
coil  the  magnetic  field  which  is  set  up  about  the  coil  con- 
verts the  iron  core  into  an  electro-magnet  which  attracts 


INDUCTION  COIL 


83 


the  metal  head  of  the  spring  and  breaks  the  contact  at  the 
adjustable  screw;  contact  being  broken  the  current  at  that 
instant  ceases  to  flow  in  the  coil  and  the  core  loses  its 
magnetism,  therefore  the  metal  head  of  the  spring  swings 
away  from  the  core,  and  in  doing  so,  by  its  own  momentum 
once  more  establishes  contact  by  touching  the  metal  point 
of  the  screw.  This  process  repeats  itself  in  rapid  succession, 
making  and  breaking  the  contact  and  in  this  way  induced 
currents  are  established  and  increased  in  the  magnetic 
field  about  the  primary  coil  which  also  intensifies  the  electro- 
magnetic force  of  the  core.  This  simple  form  of  induction 
coil  does  not  admit  of  any  regulating  of  vibratory  current 


/rod  CoRe 


Adjustable  Screw 

Induction  coil. 


set  up  by  make  and  break,  and  the  force  of  the  induced 
current  established  in  the  magnetic  field  about  the  core  will 
depend  on  the  strength  of  the  battery  which  is  producing 
the  primary  current.  The  current  from  two  Leclanche 
cells  in  such  a  coil  will  often  induce  a  maximum  vibratory 
current  greater  than  one  can  bear  when  the  terminals  are 
held  in  the  hands.  The  maximum  E.  M.  F.  produced  in 
both  coils  is  higher  than  the  battery  supplying  the  energy 
to  the  apparatus. 

There  are  many  devices  in  the  arrangement  of  the  coil 
and  the  core  by  which  the  current  strength  can  be  regulated. 
This  is  done  by  introducing  resistance  into  the  current  to 
control  the  current  strength  in  such  manner  that  it  can  be 


84  ELECTRO-PHYSICS 

varied,  or  by  resistance  introduced  into  the  primary  coil 
which  can  be  adjusted  to  vary  the  induced  current.  This 
latter  is  usually  done  by  having  a  movable  adjustable  core 
or  a  movable  secondary  coil,  or  a  brass  tube  to  slide  over 
the  core  or  a  combination  of  these  may  be  used. 

A  simple  form  of  induction  coil  in  which  the  current 
strength  can  be  regulated  consists  of  a  primary  coil  as 
already  described,  but  a  stationary  magnet  is  introduced 
instead  of  the  core.  The  current  from  a  battery  passes  to 
a  stationary  upright  to  which  is  attached  a  spring  which 
is  in  contact  with  an  adjustable  screw,  from  the  screw  it 
passes  to  the  primary  coil  which  is  wound  on  a  bobbin, 
the  return  wire  is  wound  around  a  stationary  core  fixed 
under  the  spring  and  from  this  it  is  taken  to  the  other  pole 
of  the  battery;  this  second  core  then  serves  to  interrupt 
the  current  in  the  same  way  as  described  above. 

Secondary  Coil. — A  secondary  coil  is  wound  with  a  great 
number  of  turns  of  insulated  wire,  and  slides  over  the  main 
primary  coil  so  that  it  is  in  the  magnetic  field  and  can  be 
passed  completely  over  the  primary  coil  or  drawn  away 
to  cover  only  a  very  small  part  of  the  end  of  it.  When 
the  circuit  is  closed  the  current  acts  on  the  coil  as  already 
described  and  the  strength  is  varied  by  moving  the  sliding 
secondary  coil.  The  secondary  coil  becomes  charged  with 
induced  current  which  on  make  is  in  the  same  direction 
and  on  the  break  is  in  the  opposite  direction  to  the  flow  of 
the  primary  current,  by  sliding  the  secondary  coil  over 
the  primary,  or  pulling  it  away,  the  induced  current  is 
varied  and  the  strength  of  the  vibratory  current  from  the 
coil  is  increased  or  decreased  by  the  regulation  of  the  in- 
tensity of  the  magnetic  field  and  induced  current  set  up 
about  the  coil. 

The  arrangements  of  the  wires  of  an  induction  coil  are 
best  understood  by  diagram;  by  following  out  the  lettering 
of  the  figures  which  is  the  same  in  both  diagrams,  the 
course  of  the  current  and  its  action  on  the  secondary  coil 
and  the  magnet  are  easily  comprehended.  The  diagrams 
are  from  Lewis  Jones'  book.     "One  pole  of  the  battery 


INDUCTION  COIL 


85 


is  connected  to  the  coil  at  A.  The  current  then  passes 
by  the  adjusting  screw  B,  the  vibrator  //,  and  the  sup- 
port  K,  to    a    magnet    D,   which    actuates    the    contact- 


Arrangement  of  wires  of  an  induction  coil. 

breaker.  After  traversing  this  the  circuit  gives  off  a  branch 
to  the  binding  screw  P,  and  is  continued  to  the  primary 
coil  E  E,  the  return  wire  from  which  again  gives  off  a  branch 

Fig.  25 


Induction  coil. 


to  the  secondary  binding  screw  at  P,  and  is  then  con- 
tinued to  the  other  pole  of  the  battery.  The  two  binding- 
screws  at  P  are  thus  in  connection  with  the  two  ends  of  the 


86  ELECTRO-PHYSICS 

primary  coil,  and  by  means  of  electrodes  attached  to  them 
the  patient  may  be  treated  with  the  primary  current  of  this 
coil.  The  secondary  coil  F  is  wound  on  a  separate  hollow 
bobbin  and  has  its  terminals  at  S.  This  bobbin  is  made 
to  slide  like  a  sledge  on  guides,  so  that  it  can  be  made  to 
approach  or  recede  from  the  primary  coil.  At  G  a  handle 
is  seen  attached  to  the  iron  core  which  can  slide  in  and 
out  of  the  primary  coil  and  so  further  modify  the  electro- 
motive force  induced  in  the  primary  and  secondary  coils  by 
varying  the  strength  of  their  magnetic  field." 

It  can  be  readily  seen  from  these  diagrams  that  when 
the  circuit  is  closed  the  current  passes  through  the  coil 
and  returns  by  way  of  the  magnet  and  renders  it  electro- 
magnetic, and  it  then  attracts  the  vibrator  which  causes 
the  break  in  the  current,  the  magnet  at  that  instant  loses 
its  electro-magnetic  force  and  releases  the  vibrator  which 
springs  back  into  contact  with  the  adjusting  screw,  and 
once  more  closes  the  circuit.  This  is  repeated  in  rapid 
succession.  The  adjusting  of  the  screw  and  the  sliding 
in  and  out  of  the  secondary  coil  regulates  the  frequency 
and  the  strength  of  the  vibrations. 

The  secondary  coil  is  generally  constructed  of  many 
thousands  of  turns  of  wire  according  to  the  strength  of 
E.  M.  F.  desired,  the  more  turns  the  greater  the  induced 
electro-motive  force;  the  resistance  of  so  many  turns  of 
wire  is  overcome  by  the  great  increase  in  the  induced  E. 
M.  F.  The  magnetic  field  and  induced  current  are  in- 
creased quite  out  of  proportion  to  the  resistance  by  the 
increasing  of  the  number  of  turns  in  the  coil. 

Instruments  have  been  devised  for  regulating  the  fre- 
quency of  vibrations  of  the  induction  coil;  by  altering  the 
screw  contact  breaker  and  altering  the  tension  of  the  spring 
slow  or  frequent  interruptions  are  obtained.  The  Wagner 
hammer  (Fig.  26)  is  one  of  these.  The  current  passes 
through  the  electro-magnet  which  attracts  the  hammer 
and  breaks  the  contact  from  the  adjusting  screw  C  on  the 
same  principle  as  the  vibrator  and  adjusting  screw  already 
described,  by  lengthening  or  shortening  the  distance  be- 


INDUCTION  COIL 


tween  the  contact  of  the  screw  and  the  hammer  the  vibra- 
tions are  increased  or  decreased  and  regulated  in  numbers, 
the  farther  away  the  contact  point 
is  the  slower  will  be  the  vibrations,  Fig.  26 

the  interruptions  of  the  current 
being  regulated  by  this  screw.  The 
regulation  shown  in  the  illustration 
has  an  additional  device  for  slow 
interruptions,  the  bent  wire  carry- 
ing the  adjustable  weight  K  can 
be  lengthened  by  moving  the  ad- 
justment K  which  alters  the  fre- 
quency of  interruptions. 

The  faster  the  interruptions  of 
the  current  by  the  action  of  the 
hammer  the  less  painful  are  the 
shocks;  the  proper  regulation  of 
the  vibrations  on  medical  coils  is 
an  important  factor  in  their  use.  Wagner  hammer. 


z. 


Fig.  27 


Dubois-Reymond  coil. 


88  ELECTRO-PHYSICS 

Mercury  and  electrolytic  interrupters  are  now  employed  in 
large  coils,  for  high-frequency  and  rc-ray  work.  The  primary 
cells  used  for  working  small  induction  coils  are  the  bichro- 
mate and  Leclanche,  one  cell  of  the  former  or  two  of  the 
latter  produce  ample  current  for  this  purpose. 

Fig.  27  shows  a  Dubois-Reymond  coil  with  a  scale  and 
adjustable  interrupter  for  slow  and  quick  vibrations,  the 
primary  coil  consisting  of  700  turns  of  wire  and  the  secondary 
coil  5000  turns. 


DYNAMO  CURRENTS. 

Continuous  Current. — In  speaking  of  the  continuous  current 
it  should  be  remembered  that  the  current  from  dynamos 
is  not  truly  continuous,  being  really  a  series  of  overlapping 
waves,  but  these  are,  in  a  good  machine,  so  slight,  that 
it  is  usually  known  as  continuous;  strictly  speaking  con- 
tinuous current  is  obtained  from  batteries. 

The  continuous  current  from  the  main,  which  constitutes 
a  large  proportion  of  the  electric  supply  in  commerce,  is 
made  by  converting  mechanical  power  into  electrical 
power  by  means  of  the  Dynamo. 

The  Dynamo.- — The  principal  parts  of  a  dynamo  are 
the  field  magnet,  the  armature,  and  the  commutator  or 
collecting  brushes.  The  field  magnet  is  built  into  the  dynamo 
machine  and  consists  of  a  sort  of  iron  core,  built  up  of  a  series 
of  thin  plates  insulated  from  one  another  to  prevent  "eddy 
currents,"  wound  with  a  coil  around  it  which  receives 
current  from  the  armature  to  make  it  electro-magnetic 
when  the  machine  is  working,  on  the  principle  of  the  in- 
duction coil;  it  also  becomes  a  permanent  magnet  to  an 
extent  sufficient  to  start  the  dynamo  with  a  few  turns  of 
the  armature.  It  is  so  constructed  that  the  armature  is 
received  into  two  hollowed-out  surfaces  of  the  opposing 
poles  of  the  magnet,  the  space  between  the  magnet  and 
the  armature  becomes  a  powerful  magnetic  field  when  the 
dynamo  is  working. 


DYNAMO  CURRENTS 


89 


The  poles  of  this  electro-magnet  are  permanently  set 
north  and  south. 

The  armature  is  constructed  in  some  dynamos  of  two 
insulated  metallic  rings  on  a  shaft  which  fits  into  the  hol- 
lowed space  between  the  poles  of  the  field  magnet  so  that 
a  small  space  is  left  between  it  and  the  electro-magnet; 
it  is  also  often  constructed  of  an  iron  core  upon  which  is 
wound  insulated  conductors  so  contrived  as  to  fill  the 
space  between  the  magnetic  poles  without  touching  the 
magnet,  as  shown  in  Fig.  28. 


Fig.  28 


Field  - 

Magnet 


Arm  a  tun 

Brush 

Commutator^ 
Brustf 

Magnetic  Coil 


Plan  of  dynamo. 

On  a  continuous  current  dynamo  there  is  a  commutator 
which  consists  of  a  number  of  copper  bars  insulated  from 
each  other  and  mounted  in  the  form  of  a  cylinder  through 
which  the  insulated  shaft  passes,  the  number  of  bars  cor- 
respond to  the  number  of  coils  in  the  armature  to  which 
they  are  also  attached. 

The  Collecting  Brushes  consist  of  two  copper  gauze 
brushes  or  carbon  blocks  which  are  in  contact  with  the 
commutator,  set  opposite  one  another  on  the  commutator; 
when  the  dynamo  is  in  motion  the  segments  of  the  com- 
mutator pass  in  rapid  succession  under  the  brushes  which 
collect  the  current  generated  in  the  machine  and  conduct 
it  from  the  dynamo  by  wire  connections  attached  to  the 
brushes.  The  commutator  converts  the  alternating  current 
set  ;up  by  the  action  of  rotating  the  insulated  conductor 
in  the  magnetic  field,  into  a  continuous  current. 


90 


ELECTRO-PHYSICS 


The  current  which  is  generated  in  the  armature  passes 
into  the  external  circuit  and  also  induces  a  current  in  the 
coil  around  the  electro-magnet  rendering  it  electro-magnetic 
when  the  dynamo  is  in  motion. 

There  are  two  forms  of  dynamo  winding,  the  series 
wound  and  the  shunt  wound  dynamo. 

In  the  series  wound  machine  the  current  passes  from 
one  brush  through  the  field  magnet  coil,  then  through 
the  external  circuit  back  to  the  other  brush. 


Fig.  29 


Fig.  30 


Plan  of  series  wound  action. 


Plan  of  shunt  wound  action. 


In  the  shunt  wound  dynamo  the  current  passes  in  two 
distinct  loops,  the  first  from  one  brush  around  the  field 
magnet  and  back  to  the  other  brush,  the  second,  which  is 
the  stronger  current,  passes  through  the  external  circuit 
only;  these  two  are  separate  currents  connected  in  parallel. 
Shunt  wound  motors  are  the  type  usually  used  in  dental 
engines,  lathes,  and  motor  transformers. 

The  dynamo  is  a  reversible  machine,  that  is,  if  it  re- 
ceives current  from  another  source  it  will  itself  become  a 
motor  transmitting  force  but  in  the  reverse  direction. 
Take,  for  example,  a  small  dynamo  such  as  is  sometimes 
used  to  generate  current  to  charge  accumulators,  which 


DYNAMO  CURRENTS  91 

is  usually  driven  by  some  form  of  mechanical  power  like 
a  water  or  gas  engine,  if  the  driving  power  is  disconnected 
and  the  current  from  the  charged  accumulators  switched 
on,  the  dynamo  will  work  as  a  motor  but  in  reverse  direc- 
tion as  long  as  current  is  supplied  to  it;  in  other  words,  it 
converts  mechanical  power  into  electric  current,  but  if 
supplied  with  current  from  another  source  it  becomes  a 
motor  transmitting  power. 

Alternating  Current. — This  current  from  dynamos  is  one, 
as  indicated  by  the  term,  which  alternates.  The  flow  of 
current  rises  to  maximum  in  one  direction  then  falls  to 
zero  and  rises  to  maximum  in  the  opposite  direction;  the 
time  which  elapses  between  the  rise  in  one  direction  from 
zero  to  maximum  and  back  to  zero  is  called  a  semi-cycle, 
and  the  time  which  elapses  from 
the  rise  in  the   opposite  direction  Fig.  31 

from  zero  to  maximum  and  back 
to  zero  is  the  other  semi-cycle,  so 
that  the  cycle  is  completed  in  the 
time  occupied  from  the  rise  in  one 
direction  to  the  commencement  of 
the  rise  again  in  the  same  direction. 
These  semi-cycles  correspond  respec-  Double  semi-curve 

tively  with  the  passage  of  the  coil 

through  the  north  and  south  poles  of  the  electro-magnet. 
The  time  occupied  by  a  cycle  in  a  dynamo  therefore 
depends  on  the  rate  of  the  revolutions,  in  some  machines 
the  cycles  are  regulated  at  60  cycles  per  second,  and  are 
perfectly  uniform  in  number  of  alternations.  The  change 
from  one  direction  to  another  in  an  alternating  machine 
occupies  an  exceeding  short  space  of  time,  as  is  shown  by 
the  foregoing,  and  in  well-made  dynamos  is  quite  regular. 

The  current  from  an  alternating  machine  is  often  spoken 
of  as  a  sinusoidal  current  indicating  the  curves  which 
would  be  marked  out  by  an  instrument  made  to  register 
the  sine  curve. 

Suitable  transformers  are  required  for  whatever  the 
source  of  current  to  convert  the  current  into  a  smooth 


92  ELECTRO-PHYSICS 

wave-like  alternating  current  as  used  in  medical  work,  and 
is  much  less  painful  and  more  effective  for  many  purposes 
than  the  sharp,  jerky  current  of  a  faradic  coil.  The  alter- 
nating current  from  the  main  is  the  only  kind  supplied  by 
many  installations  in  country  towns  for  lighting  purposes; 
it  is  cheaper  to  install  because  of  the  ease  and  simplicity 
with  which  it  is  transformed  from  one  potential  to  another, 
and  also  the  copper  cables  used  for  the  mains  are  much 
smaller  than  for  continuous  current.  The  current  passes 
through  those  cables  at  enormous  volt  pressure  and  is 
transformed  when  installed,  into  100  or  110  volts  by  a 
transformer  which  reduces  the  voltage  and  increases  the 
amperage. 

The  current  from  alternating  dynamos  cannot  be  used 
as  such  for  charging  accumulators,  ionic  medication,  or 
cataphoresis,  but  as  has  been  stated  is  used  for  driving 
motors,  heating  cauteries,  lighting,  rotating  high-tension 
transformers  for  arrays,  and  for  high  frequency. 

Transformers. — A  continuous  current  can  be  transformed 
into  alternating  by  means  of  a  motor  working  as  a  dynamo 
(motor-dynamo)  and  the  alternating  can  be  made  con- 
tinuous by  a  similar  instrument.  The  volts  can  be  re- 
duced and  the  amperes  increased,  or  vice  versa.  It  has 
been  shown  that  in  the  induction  coil  the  electro-motive 
force  of  the  secondary  coil  depends  on  the  ratio  of  turns 
in  the  secondary  coil  to  the  primary;  if  the  secondary 
coil  has  four  times  the  number  of  turns,  the  E.  M.  F.  will 
be  approximately  four  times  that  of  the  primary,  and  if 
it  has  one  quarter  the  number  of  turns  that  the  primary 
has,  the  E.  M.  F.  will  be  about  one-fourth  that  of  the  pri- 
mary. At  the  same  time  the  current  strength  (the  amperes) 
will  be  affected  to  the  same  extent  in  the  opposite  direction; 
a  high  E.  M.  F.  by  this  arrangement  can  produce  a  very 
low  current  strength  or  a  low  E.  M.  F.  a  very  high  amperage. 
A  transformer  can  be  designed  to  produce  a  current  strength 
of  one  ampere  at  100  volts  or  100  amperes  at  one  volt,  or 
can  be  made  to  convert  one  into  the  other. 

An   alternating   current  from   the  main   can   be  trans- 


TRANSFORMERS 


93 


formed  by  induction  into  one  of  low  voltage  and  high 
amperage,  for  example  2000  volts  and  one  ampere  can  be 
transformed  into  100  volts  and  20  amperes. 


Fig.  32 


Secondary  Coil 


-Primary  Coil 
Electro-magnet' 


Alternating  current  transformer. 


As  shown  in  Fig.  32,  the  transformer  is  in  the  form  of 
an  induction  coil,  the  principle  is  the  same,  but  this  is  a 
closed-circuit  transformer  and  a  much  more  efficient  ma- 
chine than  the  induction  coil.  It  consists  of  an  iron  core, 
which  is  the  electro-magnet,  a  primary  coil  through  which 
circulates  the  alternating  current  and  a  secondary  coil 
which  is  in  the  magnetic  field  and  is  not  wound  around  the 
primary  but  around  a  different  part  of  the  magnet,  and 
receives  the  induced  current.  The  E.  M.  F.  induced  in 
the  secondary  coil  can  be  regulated  by  the  turns  in  the 
coil  in  ratio  to  those  in  the  primary  as  has  been  explained 
elsewhere.  Transformers  for  alternating  currents  are 
especially  useful  for  cautery,  mouth  lamps,  hot  air,  root 
driers,  or  syringe. 


94  ELECTRO-PHYSICS 

The  principle,  as  explained,  of  reducing  the  volts  and 
increasing  the  amperes  places  the  current  for  these  pur- 
poses entirely  in  control.  By  placing  a  regulating  rheostat 
in  the  secondary  circuit  the  current  which  has  been  trans- 
formed may  be  regulated  to  suit  the  kind  of  cautery  or 
lamp  or  other  instrument  which  it  is  proposed  to  use,  by 

Fig.  33 


Transformer. 

varying  the  resistance.  The  rheostat  can  be  regulated  to 
heat  a  cautery  loop  requiring  2  amperes  or  be  adjusted  to 
increase  the  current  materially  to  heat  a  much  larger  loop. 
Transformers  are  also  used  for  converting  the  alter- 
nating current  into  high  voltage  and  small  amperage  for 
high-frequency  appliances.  They  are  especially  adapted 
for  this  purpose,  for  the  current  being  alternating,  can  be 


BATTERIES  95 

used  from  the  main  without  interrupters.  For  jc-ray  work 
an  alternating  current  when  transformed  must  be  made 
unidirectional  before  it  can  be  used  in  the  tubes. 

BATTERIES. 

The  construction  of  galvanic  cells,  their  chemical  action 
during  the  production  of  current,  and  the  methods  of  con- 
necting them  to  obtain  various  current  strength  has  already 
been  described.  It  has  been  pointed  out  that  Leclanche 
cells  are  the  most  practical  and  most  lasting  form  of  voltic 
cell,  because  no  change  takes  place  within  the  cell  when 
the  circuit  is  open. 

There  are  many  forms  of  batteries  from  which  a  con- 
tinuous current  is  obtained  for  most  kinds  of  dental  electro- 
therapeutic  work. 

A  useful  battery  consists  of  18  or  24  small  Leclanche 
dry  cells  which  just  fit  into  an  oak  box  made  for  the  pur- 
pose, the  cells  are  connected  in  series  and  the  current  is 
controlled  by  a  crank  cell  collector  by  which  one  or  the 
whole  battery  of  cells  can  be  turned  on  by  switching 
around  the  spring  of  the  crank  on  to  the  studs  of  the  col- 
lector. The  current  passes  from  the  controller  to  a  sliding 
shunt  rheostat  and  from  this  to  a  milliampere-meter  from 
which  it  goes  to  one  of  the  terminals  of  the  battery,  the 
other  terminal  is  set  parallel  with  the  former  and  to  these 
the  conducting  wires  are  attached  for  using  the  current. 

The  battery  also  is  provided  with  a  current  reverser,  a 
very  necessary  and  convenient  appliance  for  ionization.  A 
well-fitting  cover  keeps  the  battery  free  from  dust,  and  a 
drawer  in  the  side  to  keep  electrodes  and  wires  handy  for 
use.  In  using  the  battery  all  the  cells  should  be  switched 
on  and  the  current  regulated  through  the  rheostat,  which 
is  finely  graded  and  turns  on  the  current  very  gradually 
by  sliding  the  contact  shunt  along  the  metal  bar. 

A  battery  should  not  be  used  for  ionization  or  cata- 
phoresis  without  a  rheostat,  because  the  cell  selector  alone 
switches  on  too  much  current  at  a  time,  with  the  conse- 


96 


ELECTRO-PHYSICS 


quence  that  a  painful  shock  is  experienced  when  each  cell 
is  added  to  the  circuit.  Most  of  these  batteries  are  made 
and  sold  by  instrument  makers  with  only  the  controller, 
but  a  rheostat  should  be  insisted  on  if  good  results  are 
desired. 

Fig.  34 


Galvanic  battery. 


The  current  from  a  battery  of  18  or  24  Leclanche  cells 
works  out  according  to  Ohm's  law  as  follows:  presuming 
the  E.  M.  F.  of  each  cell  to  be  1.5  volts,  which  is  very 
nearly  correct,  and  the  internal  resistance  (r)  to  be  3  ohms, 
with  a  patient  in  circuit  of  1500  ohms'  resistance  (R)  the 
current  strength  (C)  would  be 


18  cells  X  1.5  volts 
R150b^+lr3~X  18) 


=  0.017  amperes  =  17  ma. 


BATTERIES  97 

Seventeen  milliamperes  is  a  great  deal  more  current 
than  is  required  for  ionization  of  the  penodental  membrane, 
so  that  the  E.  M.  F.  from  such  a  battery  is  ample. 

A  battery  of  24  cells  on  the  same  method  of  calculating 
will  produce: 

E.  M.  F.  24  X  1.5 

C  =  ~R+7~  =  f5Q0  +  (3  X  24)   "  °-022  amp^reS  =  22  ma- 

The  current  from  a  voltic  cell  battery  is  a  continuous 
and  smooth  current,  much  more  so  than  from  any  working 
dynamo  from  which  there  is  a  certain  amount  of  pulsation, 
although  not  sufficient  to  be  perceptible  to  a  patient  with 
a  well-regulated  rheostat  volt  selector  on  the  switchboard, 
especially  as  the  current  is  always  passed  through  a  lamp 
resistance  in  current.  Some  dentists,  however,  prefer  the 
battery  to  the  switchboard. 

Home-made  Battery. — A  dentist  should  know  how  to 
construct  his  own  battery.  This  is  a  simple  matter  with  a 
slight  knowledge  of  the  construction  of  the  parts  and  the 
path  the  current  should  take.  A  battery  which  the  author 
used  for  a  number  of  years  and  was  one  of  the  most  satis- 
factory he  ever  possessed  was  made  by  himself  as  follows: 
Place  24  Lelanche  dry  cells  in  a  small  box,  which  will  just 
hold  that  number,  connect  the  cells  in  series  with  red  cov- 
ered bell  wire,  that  is,  join  the  zinc  of  No.  1  cell  to  the 
carbon  of  No.  2  and  so  on  until  all  are  connected,  that  will 
leave  the  first  carbon  and  the  last  zinc  unconnected,  to  each 
of  these  attach  a  wire  two  yards  long  but  let  the  first  wire 
be  blue  and  the  last  be  red  to  distinguish  them.  The  wire 
from  the  first  carbon  will  be  the  positive  pole  and  the 
other  the  negative  pole  of  the  battery.  Place  the  box  in 
the  left  hand  corner  of  the  shelf  in  the  lower  portion  of 
the  cabinet  and  bore  two  holes  an  inch  apart  about  6  inches 
above  the  cells  in  the  back  of  the  cabinet,  through  these 
holes  pass  the  two  wires.  Get  a  neat  polished  board  of 
the  same  wood  as  the  cabinet  made  in  the  form  of  a  shallow 
tray  (^  inch  deep),  to  fit  the  side  of  the  cabinet  which  is 
nearest  to  the  operator  as  he  stands  by  his  chair;  to  this 
7 


98 


ELEC  TRO-PH  YSICS 


board  first  assemble  a  millianipere-meter,  shunt  rheostat, 
current  reverser,  and  two  screw  terminals  with  the  poles 
marked  on  them.  These  all  have  contact  screws  which 
pass  through  the  board  to  the  tray-like  surface  at  the  back 
where  the  connections  with  the  battery  are  made  with 
insulated  wire  in  the  following  manner: 

Fig.  35 


Switchboard  with  parts  assembled. 


To  the  — terminal  connect  the  red  wire  from  the  battery. 

To  the  distal  end  of  the  contact  rheostat  attach  the 
blue  wire,  connect  the  other  end  of  the  rheostat  with  one 
upright  of  the  milliampere-meter  and  from  the  other  up- 
right take  a  wire  to  the  +  terminal  screw.  The  battery 
is  now  complete,  but  for  a  current  reverser  which  can 
easily  be  included  if  desired,  but  which  makes  this  de- 
scription a  little  more  complicated,  and  has  not  been  in- 
cluded in  the  description,  which  it  is  desired  to  make  as 
simple  as  possible.  The  board,  when  the  several  parts  are 
connected  up,  is  screwed  on  to  the  side  of  the  cabinet,  and 


SWITCHBOARDS 


99 


the  outfit  is  a  fixture  from  which  the  current  can  be  switched 
on  at  will.  Such  a  battery  will  supply  current  for  ioniza- 
tion, gold  plating,  and  many  kinds  of  work  for  which  an 
ordinary  continuous  current  is  desired  in  dental  practice. 


Fig.  36 


Switchboard  for  current  from  a  battery. 


The  cells  last  about  eighteen  months  or  two  years  ac- 
cording to  the  size.  When  they  are  worn  out  they  are 
easily  replaced  by  new  ones  at  a  nominal  cost.  Leclanche 
wet  cells  can  be  used  in  the  same  manner  and  they  last 
forever  with  the  renewal  of  the  zincs  when  required,  and 
occasional  recharging  with  sal  ammoniac,  but  they  take  up 
more  room  and  are  not  as  clean  as  the  dry  cells. 

This  battery  can  be  made  on  the  same  principle  and 


100  ELECTRO-PHYSICS 

placed  in  a  portable  box  instead  of  being  stationary  as 
described. 

Switchboard  for  Voltic  Cell  Battery. — The  current 
from  a  cell  battery  can  be  used  from  a  switchboard  intended 
for  current  from  the  main  with  a  slight  alteration  of  the 
path  of  the  wires.  In  this  case  larger  Leclanche  cells  will 
be  required,  as  the  resistance  of  the  shunt  rheostat  is  some- 
what greater  than  the  small  rheostat  made  for  batteries. 
For  this  twenty  to  thirty  large  size  Leclanche  wet  cells  in 
series  will  be  best.  These  must  be  connected  to  the  switch- 
board the  same  as  for  current  from  the  main.  The  lamp 
resistance  must  be  dispensed  with,  but  otherwise  the  path 
of  the  current  is  the  same.  This  kind  of  board  should  be 
a  great  convenience  for  dentists  in  towns  where  the  current 
is  an  alternating  one  or  for  those  who  prefer  the  current 
from  a  battery.  The  cells  can  be  concealed  in  the  cabinet 
where  they  are  easily  reached  and  attended  to. 

Cautery  Battery. — For  cautery  and  light  a  battery 
is  required  which  will  produce  high  amperage;  for  this 
purpose  the  cells  are  connected  in  parallel.  Four  to  six 
large  cells  of  the  acid  electrolyte  type  so  arranged  that 
the  elements  can  be  lifted  out  of  the  chemical  electrolyte 
when  the  cautery  is  not  required,  constitute  a  lasting  and 
serviceable  cautery  battery.  Cells  in  parallel  act  like 
one  large  cell  with  large  zinc  surface,  producing  current  as 
if  contained  in  one  cell,  only  the  resistance  is  lessened  by 
having  several  cells  and  the  current  is  collected  more  effec- 
tively, the  voltage,  however,  is  affected  in  the  reverse,  it 
remains  the  same  as  from  one  cell.  This  has  already  been 
explained. 

The  heating  of  the  cautery  loop  depends  on  the  voltage 
and  internal  resistance  of  the  battery,  and  in  constructing 
such  a  battery  this  must  be  very  low  in  order  that  a  very 
large  current  may  be  taken  from  it.  The  current  strength 
can  be  augmented  by  adding  cells  in  series  with  each  of 
those  in  parallel,  or  by  connecting  two  equal  numbers  in 
parallel  and  then  these  two  groups  in  series;  by  this  ar- 
rangement the  current  from  a  number  of  cells  is  produced 
with  the  resistance  reduced  as  if  from  cells  in  series. 


CAUTERY  BATTERY 


101 


Where  the  main  current  is  installed  the  cautery  from  a 
switchboard  is  much  more  satisfactory,  but  the  resistance 
must  be  constructed  to  take  large  currents. 


Fig.  37 


Cautery  battery  of  cells. 


102 


ELECTRO-PHYSICS 


Accumulator  Battery. — For  cautery  work  and  lighting 
small  mouth  lamps,  antrum  lamps,  and  working  the  dental 
engine,  this  form  of  battery  is  one  of  the  most  useful.  The 
principle  of  the  accumulator  cells  has  already  been  de- 
scribed. For  cautery  two  to  six  cells  are  connected  in 
parallel  and  they  need  not  be  of  large  size,  the  cells  have 
an  E.  M.  F.  of  2  volts  each  and  the  current  strength  will 
vary  according  to  the  capacity  of  the  cells.    When  formed 


Fig.  38 


lator  battery  for  cautery. 


into  a  battery  there  should  be  a  sliding  contact  rheostat 
to  turn  on  the  current  gradually  to  suit  the  size  of  the 
cautery  or  lamp  that  is  being  used.  Many  of  the  small 
batteries  have  a  capacity  of  50  ampere  hours  which  under 
ordinary  circumstances  will  do  service  in  a  dental  surgery 
for  a  long  time.  The  accumulator  battery  is  superior  to 
a  chemical  cell  battery  for  surgical  work  or  light. 

For  working  an  ordinary  motor  dental  engine  which  is 


ACCUMULATOR  BATTERY  103 

of  shunt  wound  type  and  usually  requires  about  6  to  8 
volts  electro-motor  force,  an  accumulator  battery  of  six 
cells  connected  in  series  will  give  ample  power  to  work 
the  motor. 

The  arrangement  for  such  a  battery  consists  of  six  or 
eight  Plante  or  Faure  type  accumulator  cells  connected 
in  series;  these  should  be  placed  in  a  cool  shady  corner  of 
the  workroom  some  distance  away  from  the  workbench  so 
that  the  fumes  generated  in  charging  or  otherwise  attend- 
ing to  the  cells  will  not  affect  the  instruments  or  attendant, 
and  should  be  placed  on  a  strong  board  shelf  in  a  position 
which  will  allow  of  easy  access  to  examine  them  from  time 
to  time.  Each  cell  should  be  placed  on  a  small  board  which 
in  turn  is  placed  on  a  glass  or  porcelain  insulator  to  insure 
the  best  insulation.  When  the  cells  are  all  in  position  the 
terminals  should  be  connected  in  series,  that  is,  the  positive 
of  the  first  to  the  negative  of  the  second  and  so  on  until  all 
are  joined.  It  is  imperative  that  the  accumulator  should 
be  charged  as  soon  as  the  acid  electrolyte  is  placed  into 
the  cells.  For  this  purpose  a  small  dynamo  machine  of 
continuous  current  type,  shunt  wound,  should  be  placed 
in  the  opposite  corner  of  the  room  some  distance  away 
from  the  battery. 

The  power  for  working  the  dynamo  may  be  obtained  in 
various  ways — e.  g.,  by  gas,  hot  air,  water,  petroleum,  etc. 
A  serviceable  and  practical  method  is  by  gas  engine  of 
small  type,  such  an  engine  the  author  has  seen  working 
in  a  friend's  workroom  at  Tunbridge  Wells.  This  little 
engine  transmits  its  power  to  the  shaft  of  the  armature  of 
the  dynamo  by  a  leather  belt  and  does  the  work  of  driving 
the  dynamo  perfectly. 

The  dynamo  should  have  an  E.  M.  F.  10  per  cent,  greater 
than  the  accumulator.  The  current  collecting  brushes 
should  be  set  with  their  surfaces  perfectly  adapted  to  the 
commutator  so  that  little  or  no  sparking  takes  place  and 
pressure  should  only  be  as  much  as  is  necessary  to  insure 
perfect  contact  during  running. 

The  commutator  should  be  kept  very  slightly  greased  and 


104  ELECTRO-PHYSICS 

cleanliness  is  essential,  for  the  smallest  particle  of  grit  is 
likely  to  injure  the  machine. 

The  connections  should  be  by  insulated  wires  from'  the 
positive  of  the  dynamo  to  the  positive  of  the  first  cell  of 
the  battery  and  from  the  negative  of  the  dynamo  to  the 
negative  of  the  last  cell,  these  wires  can  be  conveniently 
placed  along  the  walls  or  ceiling  of  the  room.  An  ammeter 
should  be  placed  in  circuit  between  the  dynamo  and  the 
accumulators.  The  ammeter  is  the  guide  in  charging 
which  indicates  the  current  strength,  and  is  a  very  neces- 
sary adjunct,  for  while  overcharging  of  the  cells  in  modera- 
tion does  no  harm,  too  rapid  charging  will  ruin  the  plates 
of  the  cells. 

The  dynamo  and  power  to  drive  it,  with  the  proper 
connecting  wires  for  transmittal  of  current  to  the  cells 
having  been  arranged,  it  is  now  time  to  fill  the  cells  with 
acid  solution.  This  must  be  of  a  strength  suited  to  the 
make  and  size  of  the  cells  as  prescribed  by  the  makers. 
It  consists  of  a  solution  of  sulphuric  acid  and  water  of  a 
specific  gravity  of  about  1.170  which  rises  to  about  1.210 
when  the  cells  are  charged;  the  specific  gravity  of  the  acid 
must  be  measured  when  the  cells  are  fully  charged  and 
brought  to  the  right  degree  then.  Care  must  be  taken 
that  the  proper  poles  of  the  dynamo  are  connected  to  the 
proper  poles  of  the  battery. 

Charging  is  done  by  driving  the  current  from  the  dynamo 
through  the  cells  until  they  "boil,"  that  is  effervesce  freely; 
overcharging  in  moderation  does  no  harm  unless  the  cur- 
rent is  too  strong,  but  charging  should  be  done  continu- 
ously until  the  cells  are  fully  charged,  a  volt-meter  connected 
with  the  discharge  current  from  the  cells  determines  this, 
when  the  cells  are  fully  charged  each  one  should  have  an 
E.  M.  F.  of  2.5  or  2.6  volts,  which  will  drop  to  the  normal 
2  volts  shortly  after  charging  ceases.  If  the  charging 
potential  is  less  than  the  potential  of  the  accumulator  there 
will  be  no  charging,  no  matter  how  long  the  dynamo  may 
run.  A  slight  experience  with  charging  the  accumulator 
will  make  it  a  simple  matter. 


ACCUMULATOR  BATTERY  105 

The  battery  when  charged  will  work  the  dental  engine  in 
constant  use  for  two  or  three  weeks.  The  cells  must  not 
be  allowed  to  discharge  to  a  lower  potential  than  1.9  volts 
below  which  they  would  become  damaged,  but  should  be 
maintained  at  2  volts. 

It  remains  now  only  to  connect  the  battery  with  the 
dental  engine  which  will,  in  most  cases,  be  some  distance 
away.  It  will  therefore  be  best  to  make  the  connection 
with  large  wires  run  in  the  same  manner  as  electric  light 
wires,  small  wires  increase  the  resistance  and  therefore 
affect  the  current  strength.  Wires  of  different  colors  are 
convenient  for  marking  the  +  and  — ,  but  this  of  course  is 
not  necessary  as  it  is  an  easy  matter  to  test  the  poles  and 
determine  the  different  signs. 

A  switchboard  should  be  provided  in  the  operating  room 
by  which  the  current  from  the  battery  can  be  regulated  by 
suitable  resistance. 

The  discharge  of  the  cells  should  not  be  too  rapid  and 
must  be  regulated  by  the  number  of  plates  composing  the 
cells,  the  maximum  rate  given  for  a  15  plate  electrical 
power  storage  cell  is  28  amperes.  If  the  current  from  four 
cells  is  sufficient  to  work  the  engine  for  all  purposes  the 
other  two  cells  may  be  cut  out  so  that  the  discharge  per 
ampere-hour  is  reduced  and  the  discharge  regulated,  which 
will  add  to  the  durability  of  the  cells. 

There  is  practically  no  reason  why  an  accumulator  of 
this  description  properly  attended  to  should  not  supply 
necessary  current  for  a  surgery  for  a  number  of  years  with- 
out failure.  The  only  expense  is  the  initial  outlay,  which 
is  insignificant  compared  to  the  convenience  of  having  the 
current  in  places  where  current  from  the  main  is  not  ob- 
tainable or  is  an  alternating  current.  Those  who  con- 
template the  use  of  an  accumulator  for  this  purpose  should 
study  Sir  D.  Salomon's  book  on  the  Management  of 
Accumulators  a  practical  scientific  guide  which,  if  care- 
fully followed,  will  provide  professional  advice  on  all  points 
necessary  for  successful  use  of  the  accumulator. 

An  accumulator  battery  of  small  size  suitable  for  mouth 


106 


ELECTRO-PHYSICS 


lamps,  root-driers,  hot-air  syringe,  and  cautery  consists  of 
two  cells  put  in  a  neat  case;  each  cell  has  an  E.  M.  F. 
of  two  volts,  but  the  capacity  of  the  current  strength  in 
amperes  will  depend  on  the  size  of  the  plates.  A  useful 
size  has  a  discharge  of  about  30  ampere-hours.  The  cells 
should  be  occasionally  tested  if  it  is  suspected  that  they 

Fig.  39 


Small  portable  accumulator. 


are  about  discharged,  that  is,  the  E.  M.  F.  must  not  be 
allowed  to  fall  below  1.9  volts,  when  they  should  be  sent 
to  a  power  station  to  be  recharged.  With  this  ordinary 
precaution  the  battery  should  last  a  long  time,  and  do  all 
the  work  required  for  the  above  purposes.  For  places 
where  there  is  no  electric  light  installation  or  even  where 
there  is  but  the  operator  has  no  switchboard  for  regulating 


INDUCTION  COIL  BATTERY 


107 


the  current  supply,  a  battery  of  this  description  such  as 
supplied  by  Messrs.  Claudius  Ash  &  Sons  will  be  found 
most  useful.  Fig.  39  shows  such  a  battery,  which  is  put  up 
in  a  neat  wooden  box.  The  cells  are  of  transparent  cellu- 
loid, through  which  the  condition  of  the  plates  can  be 
seen.  This  is  a  great  advantage,  because  the  appearance 
of  the  plates  is  a  direct  indication  of  their  condition.  The 
color  of  the  plates  is  the  principal  test  for  ascertaining 
the  condition  of  the  battery.  When  fully  charged  the 
positive  plates  are  a  chocolate  or  dark  red  color,  which 
changes  when  the  accumulator  is  too  much  discharged,  to 
a  mottled  whitish  surface  from  a  sulphate  deposit  which 
coats  them.  The  negative  plates  are  a  light  slate  color 
and  may  have  a  grayish  deposit  on  the  edges  which  does 
not  necessarily  indicate  that  they  are  out  of  order. 

Fig.  40 


Dubois-Reymond's  coil,  with  two  dry  cells. 


Induction  Coil  Battery. — The  induction  coil  requires 
only  one  or  two  cells  to  work  it.  The  E.  M.  F.  is  usually 
supplied  by  two  dry  cells,  which  are  arranged  in  series  and 


108  ELECTRO-PHYSICS 

placed  in  a  box  with  the  coil,  but  a  single  large  cell  such 
as  that  used  in  Dr.  Lewis  Jones'  sledge  coil  is  all  that  is 
necessary  to'  work  the  coil.  Fig.  40  shows  a  battery  of  two 
cells  in  series  for  driving  an  induction  coil. 

This  form  of  current  is  much  used  in  medical  practice 
for  producing  sensory  and  motor  effects  and  is  most 
valuable  for  electrical  stimulation  of  living  tissue.  In 
dental  practice  it  has  been  recommended  for  stimulating 
the  gum  and  periodontal  tissues.  The  strength  of  the  coil 
and  the  character  of  the  discharges  are  dependent  on  the 
rate  of  interruptions  and  is  modified  by  the  number  of 
turns  in  the  secondary  coil  and  depend  on  this  more  than 
the  cells  producing  the  current. 


CHAPTER   V. 
BATTERY  ACCESSORIES. 

Current  Collector — Milliampere  Meter  —  Rheostats  —  Commutators — 
Rheophores — Electrodes — Rheostat  for  Direct  Current  from  Main — 
Resistance  for  Heavy  Currents — Alternating  Current  Transformers — High 
Frequency  Currents. 

Current  Collectors. — It  is  usual  for  most  continuous  cur- 
rent voltic  cell  batteries  to  be  constructed  with  a  current 
collector.  The  object  of  the  collector  is  to  vary  the  number 
of  cells  to  be  brought  into  use  at  one  time  to  suit  the  special 
case  or  to  increase  the  number  of  cells  or  collection  of  cells 
by  units  as  required.  A  battery  containing  say  24  cells  may 
be  used  with  this  contrivance  so  that  one  or  any  number  of 
cells  are  switched  into  circuit  by  turning  the  crank  handle 
of  the  collector. 

The  current  collector  consists  of  a  number  of  metallic 
studs  arranged  in  a  circle,  fitted  in  a  vulcanite  plate  which 
covers  the  cells  in  the  box.  The  studs  are  insulated  from 
each  other  and  are  connected  by  wires  to  the  corresponding 
cells  in  the  battery  in  regular  order  as  shown  in  diagram 
Fig.  41,  in  which  the  studs  numbered  1  to  8  are  connected 
to  the  positive  pole  of  cells  1  to  8;  the  negative  pole  of  cell 
No.  1  is  connected  to  a  separate  stud  numbered  0,  which  is 
connected  with  the  negative  terminal  of  the  battery.  A 
movable  crank  handle  from  the  centre  of  the  circle  of 
studs  is  made  to  fit  with  perfect  metallic  contact  on  the 
tops  of  the  studs  over  which  it  can  be  moved  to  make 
contact  with  any  of  the  studs  and  lead  of  current  from  the 
cells  corresponding  in  number  to  the  stud  in  contact.  The 
crank  is  connected  as  shown  in  the  diagram  with  the  positive 
terminal  of  the  batter}'. 


110 


ELEC  TRO-PH  YSICS 


The  cells  being  in  series  it  can  be  readily  seen  that  by 
moving  the  contact  metallic  crank  to  a  stud,  say  No.  8, 
all  these  cells  will  be  brought  into  circuit  between  the 
terminals  marked  +  and  — ,  and  in  the  same  way  when  the 
crank  is  on  No.  4  or  No.  2  or  any  stud  it  brings  into  the 
circuit  the  number  of  cells  corresponding  to  the  number 
marked  against  the  particular  stud  on  which  it  rests. 

Fig.  41 


Plan  of  current  collector. 


In  moving  the  crank  from  stud  No.  1  to  No.  2  and  so 
on  over  all  the  studs  it  increases  the  E.  M.  F.  and  current 
by  the  amount  corresponding  to  that  of  each  individual 
cell  as  the  crank  moves  to  each  adjoining  stud.  This  in- 
crease is  too  sudden  for  the  comfort  of  the  patient  in  the 
treatment  of  sensitive  tissues,  such  as  dentine,  pulp,  or 
periodontal  membrane. 

With  this  form  of  current  collector  the  cells  which  are 
connected  with  the  studs  in  the  first  part  of  the  series  are 


CURRENT  COLLECTORS 


111 


used  more  frequently  and  consequently  become  exhausted 
first,  leaving  the  latter  part  unused  or  much  less  used. 
To  obviate  this  difficulty  a  more  complicated  collector 
has  been  devised  by  which  any  section  of  the  battery  may 
be  collected.  This  is  a  Double  Collector.  Such  a  collector 
devised  by  Messrs.  Schall  &  Sons  consists  of  a  row  of  studs 
which  are  connected  with  the  cells  by  a  different  arrange- 

Fig.  42 


Double  collector. 


ment  to  the  single  collector  described.  There  are  two 
cranks  placed  on  the  same  axis  but  insulated  from  each 
other,  one  crank  is  connected  to  the  positive  terminal  of 
the  battery  and  the  other  to  the  negative.  The  zinc  of  the 
first  cell  is  connected  to  an  additional  stud  Xo.  0,  and  the 
dial  plate  is  numbered  to  correspond  with  the  cells  com- 


112  ELECTRO-PHYSICS 

prising  the  battery;  the  cranks  can  be  moved  independently 
of  each  other.  By  this  arrangement  any  portion  of  the 
battery  can  be  picked  out  by  moving  the  two  cranks  over 
studs  of  any  portion  of  the  dial,  so  that  they  include  any' 
number  of  required  cells  in  the  space  between  them,  that 
is  if  one  crank  is  on  stud  No.  2  and  the  other  on  No.  13  the 
current  would  be  obtained  from  the  intervening  11  cells 
numbered  on  the  dial.  Similarly,  if  one  crank  is  placed  on 
No.  14  and  the  other  on  No.  24  the  intervening  10  cells 
will  be  in  use,  so  that  any  group  of  cells  can  be  selected 
and  the  current  used  from  them  to  the  exclusion  of  all 
the  others. 

The  cranks  are  so  arranged  that  they  glide  from  one 
stud  to  the  next  without  actually  breaking  contact  which 
would  cause  an  unpleasant  shock  if  the  current  were  in 
use  while  they  were  being  moved. 

Milliampere  Meter  or  Milliammeter. — No  battery  is  com- 
plete without  a  milliampere  meter,  which  should  be  con- 
nected in  the  path  of  the  current  between  the  rheostat  and 
the  patient.  The  value  of  the  milliammeter  to  the  operator 
for  determining  the  current  strength,  can  hardly  be  over- 
estimated, and  no  one  should  use  the  current  for  dental 
operations  without  one.  This  instrument  has  been  greatly 
improved  of  late  by  the  invention  of  D' Arson val,  who 
applied  the  principle  of  replacing  the  permanent  magnet 
of  the  galvanometer  by  a  solenoid  which  produces  a  mag- 
netic field  when  the  current  is  passed  through  the  instru- 
ment; by  this  method  the  pointer  of  the  needle  is  made 
dead  beat,  thus  it  does  not  oscillate  when  the  current  is 
first  passed,  as  is  the  case  in  old  forms  of  galvonometer; 
its  movements  are  controlled  by  being  placed  in  a  mag- 
netic field  between  the  poles  of  a  magnet,  delicate  hair 
springs  are  attached  to  the  needle  through  which  the  cur- 
rent passes,  the  needle  deflects  gradually  from  zero,  indicat- 
ing the  current  strength  which  is  passing,  and  on  returning 
to  zero  is  kept  steady  by  the  adjustment  of  the  springs. 
The  instrument  (Fig.  43)  works  perfectly  in  all  positions, 
which  is  an  improvement  on  those  which  are  dependent 


MILLIAMPERE  METER 


113 


on  earth's  magnetisms,  and  which  therefore  require  to  be 
set  in  the  magnetic  medium. 

The  best  instruments  are  provided  with  a  Shunt,  which 
is  a  device  for  lowering  the  known  resistance  of  the  meter 
by  a  known  amount  without  influencing  the  magnetic 
field.  By  connecting  the  shunt  the  path  of  the  current  is 
open  to  a  conducting  wire  which  allows  one-ninth  the 
resistance  and  therefore  nine  times  the  current  strength 

Fig.  43 


Milliammeter. 


to  pass,  thus  nine-tenths  of  the  current  passes  through  the 
shunt  while  one-tenth  passes  through  the  instrument.  A 
second  turn  will  allow  ninety-nine  times  the  current 
strength  to  pass  by  contact  with  a  second  wire  brought 
into  the  circuit.  The  plan  of  the  instrument  is  shown  in 
Fig.  44.  The  lowest  current  strength  is  indicated  on  the 
dial  by  1,  increasing  up  to  5  milliamperes.  By  turning  the 
shunt  once  the  current  is  increased  by  the  multiple  of  10 
8 


114 


ELECTRO-PHYSICS 


and  by  turning  it  twice  it  is  increased  by  the  multiple  of 
100.    In  ordinary  dental  work  it  is  seldom  the  first  shunt  is 


Fig.  44 


Plan  of  shunt. 


Fig.  45 


Voltmeter. 


RHEOSTATS 


115 


required  and  the  second  never.  If  the  current  is  required 
for  any  other  purpose  than  ionization,  such  as  gold  plating 
for  example,  where  the  resistance  of  the  electro-chemical 
salts  in  solution  is  very  slight  compared  to  the  body,  it 
is  best  to  remove  the  milliampere  meter  and  connect  the 
path  between  the  uprights  for  holding  it,  with  a  piece  of 
copper  wire,  as  strong  current  passed  through  the  instru- 
ment tends  to  stretch  the  hair  springs  and  to  damage  the 
delicate  mechanism. 

Amperemeters  and  voltmeters  are  also  constructed  on 
the  same  principle  as  the  d'Arsonval  type  milliampere 
meter,  and  are  used  in  measuring  strong  currents  such  as 
current  from  a  small  dynamo  used  for  charging  accumulator 
battery,  and  also  for  testing  the  voltage  of  the  cells  and 
batteries,  or  the  current  passing  from  a  switchboard  for 
ionic  medications. 

Rheostats. — In  addition  to  the  current  collector  it  is 
necessary  in  most  dental  operations  to  have  a  finer  grad- 
uated scale  for  the  increase  of  the  current  strength,  the 


^L 


+ 


Fig.  46 


CtM 


HP    +o  p  ©- 

Graphite  rheostat. 


# 


switching  on  of  one  cell  at  a  time,  each  cell  of  1.5  volts, 
increases  the  current  strength  too  suddenly  in  operating 
on  periodontal  tissue  or  on  sensitive  dentine,  the  con- 
sequence is  a  painful  shock  each  time  the  crank  of  the 
collector  reaches  another  stud.  To  obviate  this  a  rheostat 
should  be  placed  in  circuit  between  the  cell  collector  and 
the  milliampere  meter,  indeed,  it  is  unnecessary  to  have  a 
current  collector  when  a  proper  rheostat  is  installed.     A 


116 


ELECT  RO-PH  YSICS 


delicate  form  of  rheostat  is  one  of  graphite  which  has  a 
resistance  of  1000  to  5000  ohms.  The  current  passes  through 
a  graphite  pencil  with  a  sliding  contact  spring  which  grad- 
ually turns  on  the  current  by  sliding  the  spring  along  a 
bar.  By  this  only  a  fraction  of  a  milliampere  of  current 
is  allowed  to  pass  at  a  time,  and  the  increase  is  not  de- 
tected until  the  current  reaches  the  desired  strength.     In 

Fig.  47 


Graphite  dial  rheostat. 

operating  on  nerve  tissue  or  sensitive  dentine  a  rheostat 
of  this  description  is  very  essential  in  order  to  increase  the 
current  without  considerable  discomfort. 

The  most  perfect  rheostat  for  resistance  of  current  from 
voltic-cell  battery,  useful  for  delicate  work  on  the  pulps 
of  teeth  or  obtaining  sensitive  tissue,  is  one   of  German 


RHEOSTATS 


117 


make,  Fig.  47.  It  is  constructed  of  a  glass  dial  which  turns 
on  a  central  pivot,  on  the  outer  circle  of  the  dial  graphite 
is  impressed  into  the  irregular  etchings  on  the  surface  of 
the  glass.  This  is  graduated  from  very  fine  to  coarser 
receptacles  for  the  graphite,  in  the  manner  shown  in  the 
figure.  The  contact  is  made  with  mercury,  which  is  let 
into  a  slot  underneath  the  dial,  and  acts  as  resistance.  By 
turning  the  glass  dial  over  the  mercury  in  contact  with 
the  graphite  conductor,  the  very  minumum  of  current 
strength  only  is  allowed  to  pass  if  the  dial  is  slowly  turned. 
The  full  resistance  of  this  instrument  is  about  20,000  ohms, 
decreasing  gradually  to  20  ohms. 


Fig.  48 


nr 


Wire  resistance. 


A  convenient  and  effective  rheostat  for  a  battery,  where 
no  current  collector  is  attached  or  necessary,  consists  of 
a  slate  core  around  which  is  wound  many  hundred  turns 
of  insulated  wire,  a  sliding  metallic  contact  spring  is  ad- 
justed to  move  over  the  coils  of  wire,  making  contact  with 
portions  of  the  wire  from  which  the  insulation  has  been 
removed,  in  such  a  manner  that  contact  with  each  turn  of 
the  wire  decreases  the  resistance  by  the  amount  of  resistance 
in  the  length  of  wire  that  passes  around  the  slate  core, 
which,  in  this  instance,  is  about  0.1  volt,  and  the  current 
strength  is  very  gradually  increased.  This  form  of  rheo- 
stat is  largely  used  on  switchboards  to  reduce  the  current 
from  the  main.  It  requires  careful  attention  in  a  damp 
climate,  for,  should  the  wire  oxidize,  the  insulation  is  liable 
to  become  imperfect,  and  the  current  brought  on  in  irregular 


118 


ELECTRO-PHYSICS 


Fig.  49 


Current  reverser. 


jerks  which  is  uncomfortable  to  the  patients.     Should  this 
occur  the  instrument  should  be  discarded. 

Current  Reverser  or  Commutator. — This  is  a  useful  addition 
to  the  equipment  of  a  battery  for  dental  purposes,  although 
not  so  essential  as  for  medical  work 
in  examining  muscle  and  nerve  re- 
actions. It  is  a  convenience,  instead 
of  changing  the  wires,  to  be  able  to 
reverse  the  poles  of  the  battery  by 
simply  moving  a  pair  of  crank  arms 
to  an  adjoining  stud  to  which  the 
reverse  wires  are  connected  inside 
the  battery.  In  ionization,  some  ions 
are  obtained  at  the  negative  pole 
(iodine  for  example)  in  using  the 
current,  when  the  reverse  to  the 
usual  current  is  desired,  simply  mov- 
ing the  crank  arm,  Fig.  49,  brings 
about  the  desired  effect. 
Rheophores  or  Conducting  Cords.— Rheophores  or  con- 
ducting cords  are  made  of  insulated  flexible  wire  finished 
off  at  each  end  with  suitable  metallic  connecting  ends  for 
attachment  to  the  terminals  of  the  battery  and  electrodes. 
They  should  be  of  sufficient  length  to  give  perfect  freedom 
in  using  the  electrodes;  two  or  two  and  a  half  yards  is  a 
convenient  length,  and  it  is  best  to  have  two  colors,  one 
for  the  positive  terminal  and  the  other  for  the  negative. 
They  are  best  made  of  several  strands  of  fine  copper  wire 
twisted  into  a  flexible  cord  which  is  insulated  by  cotton 
covering.  Cords  of  a  single  wire  covered  with  rubber  are 
sometimes  used,  but  these  are  liable  to  break  from  being 
frequently  wound  up  and  unwound  for  use,  and  should  a 
break  occur  when  the  current  is  in  use,  a  painful  and  alarm- 
ing shock  to  the  patient  occurs,  the  possibility  of  which 
must  be  carefully  guarded  against.  This  is  a  possible 
contingency  with  any  conducting  cords  which  should  be 
guarded  against  by  using  none  but  the  best  quality,  and 
seeing  that  it  is  always  in  good  order.    A  break  of  the  cord 


ELECTRODES  119 

takes  place  most  frequently  at  its  junction  with  the  attach- 
ment for  the  terminal  or  electrode,  and  if  not  discovered, 
may  lead  to  the  conclusion  that  the  current  has  failed, 
which  may  not  be  the  case;  it  is  then  advisable  to  test  the 
battery  to  decide  this  point. 

Electrodes. — These  are  the  conductors  which  convey  the 
current  to  the  body.  They  are  the  terminals  which  are 
constructed  of  some  conducting  material  specially  in- 
tended for  the  application  of  the  current  to  the  patient. 
The  positive  or  active  electrode  is  that  which  conveys  the 
current  to  the  body,  and  the  negative  or  indifferent  electrode 
is  that  by  which  the  circuit  is  completed,  or  it  might  be 
said,  by  which  the  current  leaves  the  body. 

Fig.  50 


Wrist  electrode. 

They  consist  of  all  sorts  of  shapes  and  sizes  constructed 
to  suit  the  particular  purpose  for  which  required.  In  medi- 
cal practice  these  are  very  numerous;  for  dental  work  the 
indifferent  electrode  or  the  one  to  which  the  negative  pole 
is  connected,  should  consist  of  some  unoxidizable  metal 
(or  of  carbon)  which  should  always  be  covered  with  some 
material  to  prevent  actual  contact  of  the  metal  with  the 
body,  such  as  lint  or  chamois  leather  or  any  absorbent 
material,  which  must  be  free  from  chemical  ingredient. 
Metal  should  not  be  used  uncovered  to  apply  electricity 
to  the  body  because  it  is  liable  to  cause  pain  and  inflict 
burns  or  blisters  on  the  surface  of  the  skin,  due  to  the  electro- 
lytic action  set  up  at  the  surface  of  contact. 

The  indifferent  electrode  should  consist  of  a  flat  piece 
of  metal  about  two  inches  in  diameter  to  which  is  soldered 
a  terminal  in  the  centre  for  attachment  of  the  conducting 


120 


ELECT  RO-PH  YSICS 


cord.  It  should  be  covered  with  a  pad  of  lint  which  can 
be  readily  removed  and  renewed.  A  leather  strap  with 
a  buckle  to  attach  it  to  the  patient's  wrist  completes  the 
wrist  indifferent  electrode.  It  is  essential  to  keep  the 
electrode  clean.  It  should  always  be  applied  moistened 
with  warm  water  or  a  warm  saline  solution.  It  should  be 
applied  firmly  to  the  site  of  contact,  and  kept  moist. 

Fig.  51 


Indifferent  electrode. 

Some  operators  prefer  to  apply  the  indifferent  electrode 
nearer  the  site  of  the  application  of  the  active  electrode, 
which  is  the  electrode  conveying  the  positive  electricity. 
In  application  of  the  current  to  parts  of  the  oral  cavity, 
when  it  is  desired  to  place  the  indifferent  electrode  near 
to  the  site  of  contact  of  the  other  electrode,  one  such  as  is 
shown  in  the  illustration  Fig.  51,  invented  by  Dr.  Lewis 
Jones  should  be  placed  under  the  chin  and  held  in  firm 
contact  with  that  surface.  This  electrode  possesses  the 
advantage  of  being  readily  covered  with  a  new  clean  cover 
for  each  patient.  It  is  made  in  sections  which  allow  of  a 
new  cover  being  easily  slipped  on.  Electrodes  of  this 
description  are  a  little  awkward  to  manage  at  first  but 
are  the  best  of  the  kind  for  application  to  this  part  of  the 
body. 


ELECTRODES 


121 


If  the  electrode  is  not  large  enough  or  if  it  does  not  make 
good  contact  the  current  is  liable  to  cause  blisters  to  the 
skin  at  the  site  of  contact  of  the  indifferent  electrode,  even 
when  a  small  current  is  passed.  In  the  case. of  the  hand 
electrode,  if  the  metal  is  of  small  size  and  not  grasped 
firmly  by  the  patient,  a  small  hard  white  blister  about  the 
size  of  the  head  of  a  large  pin  may  appear  at  some  point  in 
the  palm  of  the  hand,  attended  with  some  discomfort  to 
the  patient,  the  skin  dies  at  this  point  and  the  mark  will 
only  disappear  when  the  skin  is  removed  a  long  time  after. 
To  obviate  this  occurrence  place  a  carbon  electrode,  cov- 
ered with  a  couple  of  folds  of  flannel  into  a  glass  vessel 
filled  with  slightly  warm  water  and  some  sodium  chloride, 

Fig.  52 


Carbon  and  water  electrode. 


the  patient's  hand  must  be  immersed  in  the  water  and  the 
palm  of  the  hand  pressed  firmly  on  the  covered  carbon 
conductor  at  the  bottom  of  the  glass  dish.  This  is  always 
a  comfortable  form  of  indifferent  electrode,  which  patients 
appreciate,  especially  if  pain  is  experienced  by  contact  of 
other  forms  of  metal  electrodes.  The  connecting  cord 
from  a  water  electrode  should  be  rubber  insulated  copper 
wire. 

Another  form  of  indifferent  electrode  quite  well  adapted 
for  ionic  medication  consists  of  a  nickel-plated  metal  handle 
which  the  patient  holds.  This  should  have  a  moistened 
sponge  at  the  open  end  and  should  be  covered  with  stockin- 
ette or  lint  moistened  with  salt  and  water.     It  should  not 


122 


ELECTRO-PHYSICS 


be  of  brass  or  copper  as  sometimes  made,  and  should  be  of 
the  largest  size  displayed  by  makers.  This  form  of  electrode 
is  preferred  by  some  patients  as  they  seem  to  like  to  hold 


Fig.  53 


Hand  electrode. 


on  to  something;  the  epidermis  of  the  palm  of  the  hand  is 
thick  and  not  usually  sensitive  to  current  of  small  amperage 
such  as  is  usually  required  for  applications  to  periodontal 
membrane. 

Fig.  54 


The  author's  chin  electrode. 


The  chin  electrode  devised  by  the  author  consists  of  a 
nickel-plated  metallic  plate  which  fits  under  the  chin  with 
a  contact  screw  soldered  to  the  middle  and  end  pieces  to 
receive  an  adjustable  elastic  strap  which  is  intended  to 


ELECTRODES  123 

pass  over  the  head  and  hold  the  electrode  firmly  in  place. 
It  should  be  covered  with  a  pad  of  lint  next  to  the  skin, 
and  should  be  moistened  with  salt  and  water.  TJiis 
form  of  electrode  for  contact  on  the  face  is  comfortable 
and  useful  where  it  is  desired  to  lessen  the  resistance  by 
having  the   electrodes   in   close  proximity. 

Active  electrodes  convey  the  positive  current  to  the 
site  of  application.  They  consist  of  an  insulated  rubber 
or  ebony  handle  with  an  attachment  screw  at  the  one  end 
to  connect  the  conducting  cord  to,  the  other  end  should 
consist  of  an  interchanging  screw  piece  to  receive  the  par- 
ticular applicator  required;  the  electrodes  to  fit  these 
handles  should  be  of  platinum,  zinc,  or  copper,  and  shaped 
according  to  the  requirement  of  the  operation;  for  pyorrhoea 

Fig.  55 


The  author's  electrode  hand  piece. 

pockets  or  gingival  trough,  spear-shaped  metallic  points 
of  the  metals  mentioned,  5  cm.  long  by  2  mm.  wide  and 
1  mm.  cross-section.  These  should  be  interchangeable  at 
the  hand  piece  and  readily  removed  for  sterilizing.  The 
extreme  ends  should  be  rounded,  as  sharp  points  increase 
the  density  of  the  current  which  makes  it  painful.  The 
points  are  flexible  (except  zinc),  which  permits  of  them 
being  bent  to  suitable  curves  for  different  angles  when 
required  to  pass  to  the  approximal  surfaces  of  molars. 
The  shanks  of  the  points  should  be  insulated  three-quarters 
of  the  length  to  prevent  the  current  passing  to  the  lips  and 
cheeks  adjoining  the  site  of  application.     (See  Fig.  56.) 

For  root  canals,  electrodes  of  fine  copper,  platinum,  or 
steel  wire  twisted  into  a  coil  at  one  end  and  straightened 


124 


ELECTRO-PR  YSICS 


out  for  varying  lengths  of  half  to  one  inch  in  length,  the 
straight  part  for  insertion  into  the  root  canal,  and  the  coil 
to  receive  the  end  of  a  spear-shaped  point  attached  to  the 
ordinary  handle,  to  hold  it  steadily  in  position  when  being 
used  (Fig.  57). 


Fig.  56 


Fig.  57 


0 


The  author's  pyorrhoea  electrodes. 


The  author's  root  canal  electrodes. 


Copper  probes  for  fistulous  tracts  of  chronic  alveolar 
abscesses  should  be  made  with  this  coil  at  the  one  end  to 
receive  an  ordinary  electrode  with  which  to  make  contact 
when  applying  copper  ions,  as  will  be  described  later.  The 
thickness  of  these  probes  should  be  0.5  mm. 


Tongue-shaped  duplex  electrode. 


Dr.  W.  J.  Morton  recommends  a  tong-shaped  Duplex 
cataphoresis   electrode,   which   consists   of   a   pair   of   per- 


RHEOSTAT  FOR  DIRECT  CURRENT  125 

forated  disks  mounted  on  holders  shaped  as  the  diagram 
shows,  like  tongs.  Both  disks  are  active  electrodes  and  are 
intended  to  contain  the  solution  for  medication  of  two  sur- 
faces of  the  gums  or  alveolus  at  the  same  time.  Platinum 
is  the  conducting  metal  forming  the  floor  of  the  disks,  to 
which  is  soldered  copper  wire  which  passes  through  the 
insulated  holder  with  a  contact  screw  at  the  end  to  receive 
the  conducting  cord. 

Rheostat  for  Direct  Current  from  the  Main. — The  con- 
tinuous current  from  the  main  is  the  most  convenient 
source  of  supply  of  electricity  for  ionic  medication  and 
cataphoresis.  It  is  quite  safe,  notwithstanding  the  high 
E.  M.  F.,  if  only  ordinary  precautions  are  adhered  to,  and 
it  is  not  any  more  painful  to  use  than  the  current  furnished 
by  voltic  cells. 

The  current  from  the  main  must  be  reduced  to  very 
low  voltage  with  a  minimum  output  of  current  strength. 
This  is  accomplished  by  suitable  resistance  interposed  on 
the  switchboard  between  the  supply  and  the  patient.  The 
current  is  controlled  by  passing  it  through  a  coil  of  re- 
sistance wire  which  is  wound  around  a  core  of  insulator 
material,  like  slate.  Each  turn  of  wire  is  insulated  per- 
fectly from  the  next,  although  placed  very  close  to  it.  Sev- 
eral hundred  turns  of  the  wire  represents  a  resistance 
sufficient  to  reduce  the  current  of  240  volts  to  0.15  volts. 
A  lamp  is  also  placed  in  circuit  which  when  the  current  is 
switched  on,  assists  in  reducing  the  current  and  acts  as  a 
guide  to  indicate  the  presence  of  the  current  and  a  safe- 
guard against  sudden  rise  of  current  by  accident  to  the 
insulation  of  the  resistance. 

The  principle  of  the  switchboard  resistance  is  explained 
in  the  diagram;  the  current  passes  from  A  to  B  through 
the  resistance  coil.  At  B  a  contact  sliding  metallic  spring 
is  adjusted  on  a  metal  bar  over  the  coil,  this  moves  in  the 
direction  A  over  the  resistance,  the  sliding  contact  is  con- 
nected with  the  +  terminal  of  the  switchboard,  the  end  of 
the  coil  at  B  is  connected  with  the  —  terminal,  an  incan- 
descent lamp  is  also  on  the  negative  side  of  the  board.     It 


126 


ELECTRO-PHYSICS 


can  be  readily  seen  by  the  diagram  (Fig.  59)  that  the 
current  must  pass  through  the  entire  resistance  before  it 
reaches  the  contact  spring  when  it  is  adjusted  at  B,  and 
that  by  sliding  the  spring  toward  A  the  resistance  is 
gradually  reduced  and  the  current  strength  increased. 
The  E.  M.  F.  when  the  current  passes  through  the  entire 
resistance  is  only  a  fraction  of  a  volt,  as  the  spring  slides 
over  the  coil  from  B  toward  A  it  increases  the  E.  M.  F. 
very  gradually  by  about  0.1  volts  as  it  passes  over  each  turn 
of  the  wire  coil.  A  milliampere  meter,  which  should  always 
be  used,  is  placed  in  circuit  between  the  resistance  and  the 

Fig.  59 


Plan  of  switchboard  resistance. 


+  terminal  by  a  connection  to  the  metal  bar  upon  which 
the  contact  spring  C  slides.  Current  controlled  from  the 
main  by  this  method  seldom  gives  any  trouble,  as  the 
operating  chair  is  usually  perfectly  insulated,  but  it  must 
be  borne  in  mind  that  in  these  wire  circuits  if  the  negative 
pole  is  brought  in  contact  with  anything  connected  with 
earth,  when  the  circuit  is  closed,  a  severe  shock  is  liable  to 
occur  from  this  source,  even  if  the  current  at  the  positive 
pole  is  reduced  to  minimum  by  the  resistance.  For  this 
reason  it  is  dangerous  to  use  a  metallic  saliva  ejector  when 
using  the  current  in  the  mouth,  for  the  water  might  make 


GALVANIC  SWITCHBOARD 


127 


perfect  contact  with  the  earth  through  the  metallic  pipe 
connections.  No  water  pipe  or  gas  fitting  should  be 
touched  by  the  operator  or  patient  when  the  current  is 
being  used.  It  is  possible  for  very  damp  weather  to  so 
moisten  the  carpet  on  which  an  operating  chair  rests,  that 

Fig.  60 


Switchboard  for  ionic  medication. 


imperfect  contact  is  made  with  earth  and  thus  to  become 
a  source  of  contact  when  using  the  current.  This  can  be 
overcome  by  insulating  the  chair  perfectly  by  placing  the 
base  on  a  rubber  mat. 

Current  controlled  by  this  form  of  rheostat  switchboard 
(see  Fig.  GO)    is  used    for  all  kinds  of    galvanization  and 


128  ELECTRO-PHYSICS 

ionic  medication;  the  E.  M.  F.  is  reduced  and  the  current 
strength  brought  down  to  a  minimum,  and  differs  from 
the  switchboard  used  for  cautery  or  hot-air  syringe,  which 
requires  a  current  of  high  amperage  with  a  low  voltage,  and 
which  cannot  be  used  for  ionc  medicatiion. 

Resistance  for  Heavy  Currents. — The  current  which  is 
required  from  a  switchboard  for  cautery  light,  hot-air 
syringe,  water  heater,  etc.,  of  the  type  now  much  used  can- 
not be  controlled  by  wire  rheostat  resistance  inserted  in 
circuit  on  the  principle  of  the  galvanic  switchboard.  The 
resistance  in  series  which  will  permit  of  strong  enough 
current  strength  to  heat  a  cautery  loop  would  require  an 
electro-motive  force  which  would  be  sufficient  to  establish 
an  electric  arc  at  the  moment  of  breaking  the  current  in 
the  handle  of  the  cautery  which  would  destroy  the  instru- 
ment, or  should  the  platinum  loop  be  overheated  and  be- 
come fused  when  in  use,  the  danger  would  be  serious.  The 
principle  of  resistance  for  these  switchboards  is  one  which 
is  known  as  the  shunt  circuit;  it  consists  of  two  parallel 
circuits:  one  for  the  current,  which  is  required  for  the  in- 
struments, the  other  acting  as  a  shunt  circuit  in  case  of 
overheating  or  fusing  of  any  other  connection  on  the  switch- 
board; there  are  a  number  of  resistance  coils  of  thick  wire 
attached  to  the  back  of  the  switchboard  which  are  con- 
nected in  series  with  conducting  studs  at  intervals,  which 
lead  the  current  to  the  front  of  the  board,  where  several 
crank  arms  are  attached  to  switch  on  the  required  current 
for  the  different  instruments  for  which  the  particular  cur- 
rent strength  is  intended.  There  is  a  pilot  lamp  at  the 
top  of  the  board  which  indicates  the  presence  of  the  current. 
The  current  strength  of  the  different  instruments  is  regu- 
lated by  the  length,  thickness,  and  number  of  coils  in  the 
wire  which  form  the  rheostats  at  the  back  of  the  board, 
different  amperage  being  necessary  for  different  individual 
instruments  or  sets  of  instruments. 

When  the  current  is  switched  on,  a  large  amount  of  cur- 
rent is  constantly  passing  through  the  shunt  circuit  which 
of  course  is  not  used,  in  this  there  is  considerable  waste, 


ALTERNATING  CURRENT  TRANSFORMER 


129 


and  the  current  should  not  be  left  on  the  switchboard 
except  it  is  in  use.  An  illustration  of  a  switchboard  for 
heavy  currents  appears  on  p.  149. 

Alternating  Current  Transformers. — It  is  desirable  some- 
times to  change  the  alternating  current  from  the  main 
into  continuous  current,  or  to  transform  it  into  one  of  low 
voltage  and  high  amperage  for  cautery  or  lamp;  this  is 
accomplished  by  induction,  or  motor  transformers  or  by 
rectifiers. 

Fig.  61 


Transformer  for  light  and  cautery. 


By  an  induction  coil  on  the  principle  already  mentioned, 
the  current  of  high  voltage  can  be  transformed  into  one 
of  low  E.  M.  F.  and  high  current  strength,  or  by  having 
two  coils  wound  on  a  ring  of  soft  iron,  a  primary  with  a 
greater  number  of  turns  in  the  coil  than  the  secondary,  the 
current  passes  through  the  primary  and  induces  current 
in  the  secondary  which  is  in  the  magnetic  field  of  the  coil. 
Current  transformed  in  this  manner  is  used  for  cautery 
and  light.  For  producing  the  opposite  effect,  that  is,  trans- 
forming the  current  into  much  higher  E.  M.  F.,  the  winding 
9 


130  ELECTRO-PHYSICS 

of  the  coils  is  reversed,  the  primary  with  a  fewer  number 
to  turns  in  the  coil  than  the  secondary.  Current  trans- 
formed in  this  manner  can  be  used  for  high  frequency 
apparatus,  or  if  a  synchronous  commutator  in  the  secondary 
circuit  is  employed,  for  the  #-ray  work.  The  switchboards 
are  provided  with  sliding  resistance  for  adjusting  the  volt- 
age to  the  required  strength.  These  forms  of  transformers 
are  much  used  for  cautery  and  light.  They  are  sometimes 
arranged  to  give  two  or  three  different  voltages,  by  having 
two  or  three  secondary  windings  wound  on  different  parts 
of  the  iron  ring,  each  having  different  numbers  of  turns 
of  wire,  and  induce  different  currents  that  are  taken 
to  different  terminals  on  the  switchboard.  One  coil  is  of 
thick  wire  and  of  few  turns  and  gives  a  current  of  low 
voltage  and  high  amperage  for  cautery;  another  is  of 
finer  wire  and  more  turns  which  gives  a  higher  voltage 
and  a  certain  amperage  for  lighting  small  lamps;  a  third 
is  of  still  finer  wire  and  more  turns  and  gives  a  current  for 
therapeutic  work.  Current  transformed  on  this  principle  is 
readily  regulated  and  answers  the  purposes  for  which  it  is 
intended. 

To  transform  an  alternating  current  from  the  main 
into  a  continuous,  a  motor  which  works  by  the  alternating 
current  is  required.  This  is  made  to  transmit  mechanical 
energy  to  work  a  direct  current  dynamo  from  which  the 
direct  current  is  collected.  By  a  motor  transformer  a 
continuous  current  can  be  obtained  of  almost  any  desired 
electro-motive  force  and  current  strength  suited  to  wind- 
ings of  continuous  current  engines  and  lathes  or  galvanic 
switchboards,  and  other  dental  devices  for  which  a  con- 
tinuous current  is  required.  For  medical  purposes  this 
form  of  transformer  is  useful  for  spark  coils,  arc  lamps,  or 
electro-magnets,  and  it  may  be  used  for  charging  accumu- 
lators. 

Another  method  of  transforming  the  alternating  current 
is  by  synchronous  rectifier,  a  mechanical  device  which  is 
attached  to  an  alternating  current  dynamo,  by  which  the 
impulses  of  the  current  which  tend  to  pass  in  one  direction 


ALTERNATING  CURRENT  TRANSFORMER 


131 


are  arrested  at  intervals  which  correspond  to  those  im- 
pulses in  the  current,  the  current  in  the  other  direction 
passes  as  a  pulsating  undisciplined  current.  This  form  of 
rectifier  consists  of  a  magnetically  polarized  steel  rod  which 
vibrates  between  the  poles  of  an  electro-magnet  supplied 
by  the  alternating  current,  the  rod  vibrates  in  synchronism 
with  the  impulses  of  the  current,  and  in  vibrating  makes 
contact  with  two  studs  alternately.  The  current  rectified 
by  this  means  may  be  used  for  charging  accumulators. 

Fig.  62 


Motor  transformer. 


High  Frequency  Currents. — High  frequency  currents  may 
be  described  briefly  as  alternating  electric  currents  which 
discharge  with  oscillations  of  great  frequency.  The  oscilla- 
tions may  amount  to  millions  a  second  and  vary  in  conti- 
nuity and  frequency  with  conditions  of  capacity,  induction, 
and  resistance,  in  production  of  the  discharge.  It  is  beyond 
the  scope  of  this  work  to  describe  in  detail  phenomena 


132 


ELECTRO-PHYSICS 


of  high  frequency  discharges.  The  present  efficiency  of 
apparatuses  for  production  of  high  frequency  currents  is 
due  to  the  studies  and  ingenuity  of  such  authors  as  Sir 
Oliver  Lodge,  Hertz,  Tesla,  Elihu  Thomson,  and  D'Arsonval. 
D'Arsonval  discovered  the  present  day  principle  of  the 
high  tension  high  frequency  coil,  he  connected  the  internal 
armatures  of  two  Leyden  jars  with  the  terminals  of  a  sec- 
ondary  current   from   an   induction   coil;   to   the   external 

Fig.  63 


-t- 


o 


External  Armature 


Selenold 


Spark,  Gap 
0*0- 


0      /   - 


Internal  Armature 


D'Arsonval's  principle  of  high  frequency  apparatus. 


armatures  he  connected  a  spiral  of  about  twenty  turns  of 
thick  copper  wire.  To  the  internal  armatures  he  connected 
on  an  upright,  two  horizontal  metallic  rods  which  terminated 
in  rounded  ends  to  form  a  spark-gap.  He  discovered  that 
on  charging  the  condensers,  each  time  a  discharge  spark 
crossed  the  spark-gap  a  high  potential  current  with  oscil- 
lations of  a  high  frequency  was  set  up  in  the  spiral  at- 
tached to  the  external  armatures  and  that  this  form  of 


HIGH  FREQUENCY  CURRENTS  133 

current  could  be  collected  from  the  ends  of  the  coil  (see 
Fig.  63).  Many  of  the  modern  instruments  for  pro- 
ducing high  frequency  are  constructed  on  the  principle  of 
D'ArsonvaPs  discovery.  The  electrical  source  of  energy 
to  work  a  high  frequency  apparatus  is  best  obtained  from 
continuous  or  alternating  main  current  supply,  but  pri- 
mary and  secondary  batteries  can  be  used.  In  using  cur- 
rent from  the  main  the  ratio  of  electro-motive  force  and 
current  strength  must  be  altered,  this  is  accomplished  by 
induction  coil  current  interrupters,  motor  converters,  etc., 
constructed  on  the  principles  already  described.  The 
apparatus  consists  of  condensers,  spark-gap,  solenoid,  and 
resonator. 

Condensers  consist  of  two  Leyden  jars  or  glass  plate  con- 
densers constructed  on  the  principle  of  Leyden  jars.  They 
are  connected  by  contact  with  their  inner  coating  of  tin- 
foil or  metal  conductor,  with  a  secondary  coil,  or  high- 
tension  transformer  or  whatever  the  source  of  electrical 
energy  may  be.  The  spark-gay  is  formed  by  two  adjust- 
able conductors  which  are  in  contact  with  the  conductors 
attached  to  the  internal  lining  of  the  condensers,  the  spark- 
gap  is  usually  enclosed  in  some  form  of  covering  which 
deadens  the  sound  of  the  spark,  when  the  discharges  be- 
tween the  two  jars  take  place.  The  solenoid  is  a  coil  of 
copper  wire  which  is  connected  to  the  outer  covering  of 
the  condensers.  It  usually  consists  of  about  twenty  turns 
of  thick  copper  wire.  The  resonator  is  made  in  several 
forms,  and  consists  in  one  form  (D'Arsonval's)  of  four  turns 
of  thick  wire  which  is  connected  at  each  end  to  the  outer 
coating  of  the  condensers;  on  the  outside  of  this  coil,  placed 
about  two  inches  away  from  it,  is  a  secondary  coil  of  fine 
wire  made  of  a  great  number  of  turns  over  an  ebonite 
cylinder.  This  secondary  coil  induces  currents  of  higher 
tension  than  the  outer  coil  of  thick  wire. 

The  several  parts  of  the  apparatus  are  assembled  and 
mounted  on  a  small  table,  or  as  is  the  case  of  a  small  port- 
able apparatus,  in  a  strong  wooden  box.  The  usual  type 
of  apparatus  for  medical  purposes  is  shown  in  the  accom- 


134 


ELECTRO-PHYSICS 


panying  Fig.  65.  The  condensers  are  placed  on  the  lower 
platform  of  the  table,  and  are  connected  by  the  inner 
coatings  to  the  secondary  terminals  of  an  induction  coil 
worked  by  motor  interrupter,  and  also  to  the  spark-gap 


Fig.  64 


High  frequency  transformer. 


which  is  enclosed  in  a  box  inside  which  the  sparking  takes 
place  between  the  metallic  knobs,  which  are  adjustable 
to  suit  the  spark  desired. 

The  outer  coatings  of  the  condensers  are  connected 
through  the  solenoid,  from  which  the  currents  are  conveyed 
to  the  patient.    The  resonator  is  made  of  a  coil  of  copper 


HIGH  FREQUENCY  CURRENTS 


135 


wire,  which  is  wound  around  a  frame  and  placed  on  the 
top  of  the  table.  These  two  are  connected  in  different 
ways  according  to  the  make  of  the  apparatus;  some  have 
adjustable  contacts. 


Fig.  65 


Combined  high  frequency  apparatus. 


136 


ELEC  TRO-PH  YSICS 


A  milliampere  meter  of  the  hot  wire  type  (Fig.  66)  is 
usually  connected  between  the  patients  and  the  solenoid, 
or  the  resonator  of  the  high  frequency  apparatus. 

High  frequency  currents  conducted  from  the  solenoid 
to  the  body  are  of  great  magnitude.  D'Arsonval  has 
shown  by  experiment  that  an  incandescent  lamp  placed 
in  series  between  the  instrument  and  the  patient,  so  that 
the  current  must  flow  through  the  lamp  before  reaching 

Fig.  66 


Hot  wire  milliampere  meter. 

the  patient,  will  glow  brightly,  yet  no  unpleasant  sensation 
is  noticed  if  the  electrodes  are  firmly  grasped.  It  would 
be  impossible  to  pass  a  similar  current  without  serious 
effect  on  the  body. 

In  general  electrification  of  the  body  by  high  frequency 
currents  different  methods  are  adopted  for  passing  the 
current  to  the  body;  by  direct  conduction  from  the  ends  of 
the  solenoid;  by  conduction  from  one  end  of  the  solenoid 
with  the  other  end  connected  to  a  conductor  placed  in 
proximity  but  not  touching  the  patient;  and  by  auto-con- 
duction, which  consists  in  placing  the  patient  in  spiral 
wire  enclosures  large  enough  to  completely  enclose  him 
without  touching  him,  the  current  passing  through  the 
wire  enclosure  or  solenoid  is  transmitted  by  induction. 


HIGH  FREQUENCY  CURRENTS 


137 


In  the  use  of  high  frequency  currents  for  local  applica- 
tion in  dental  treatment  a  modified  apparatus  is  required. 
This  has  been  carried  out  in  one  form  by  what  is  known 
as  the  Tesla  Transformer,  principle  which  requires  no 
motor  interruptor.  The  apparatus  is  connected  to  the 
main,  continuous  or  alternating  current,  by  a  wall  plug, 
the  current  passes  through  an  arrangement  of  induction 
coils  and  a  spark-gap  which  regulates  the  potential  and 
frequency.     The  current  is  conveyed  to  the  mouth  of  the 

Fig.  67 


Victor  Gem  high  frequency  apparatus. 


patient  by  a  vacuum  glass  electrode  which  when  in  poor 
contact  with  the  tissues  produces  slight  heat,  and  if  held  a 
slight  distance  away  produces  a  small  brush  spark.  The 
sparking  gap  is  only  two  or  three  inches  wide,  which  pro- 
duces high  frequency  currents  of  sufficient  amperage  for 
treatment  of  oral  tissue. 

Such  an  apparatus  is  shown  in  the  cut.    It  is  of  American 
make,  called  the  Victor  Gem  high  frequency   coil,  Messrs. 


138  ELECTRO-PHYSICS 

Ash  &  Sons  being  the  English  agents.  Glass  vacuum 
electrodes  made  to  shapes  adaptable  to  treatment  of  the 
gums,  supplied  with  this  outfit,  are  admirably  suited  for 
the  purpose;  a  wire  conductor  passes  through  the  glass, 
conveys  the  current  and  establishes  connection  between 
the  interior  of  the  electrode  and  the  conductor. 

Another  high  frequency  apparatus  intended  for  local 
treatment  of  the  mouth  called  the  "Invictus  Portable 
High-frequency  Apparatus,"  made  by  K.  Schall  &  Son, 
consists  of  an  oak  box  about  the  size  of  an  ordinary  sixteen 
cell  battery.  Into  this  is  fitted  a  board  on  which  is  mounted 
a  small  coil  which  transforms  the  current  up  to  about 
2000  volts.  The  interrupter,  which  is  designed  on  the 
ordinary  hammer  principle,  is  specially  constructed  to 
take  the  large  currents  from  the  main.  Another  inter- 
rupter is  arranged  in  circuit  with  the  first  and  its  function 
is  to  prevent  the  first  from  receiving  too  much  current. 
Under  ordinary  circumstances  it  is  inactive,  but  when  the 
first  one  is  not  properly  adjusted,  and  therefore  passes  too 
much  current,  it  comes  into  action  and  so  prevents  the 
contacts  of  the  first  one  from  being  fused  by  the  excessive 
heat  produced  by  overloading. 

In  the  body  of  the  box  there  are  fixed  the  condensers 
and  the  inductance.  The  former  are  charged  in  the  ordinary 
way,  by  means  of  a  spark-gap  which  is  fixed  on  one  side  of 
the  box  and  they  discharge  through  the  inductance.  The 
open  part  of  this  which  resonates  to  the  closed  part  is 
brought  to  a  terminal  on  the  other  side  of  the  box,  and  to 
this  the  vacuum  electrodes  are  attached. 

The  strength  of  the  discharge  is  regulated  by  the  length 
of  the  spark-gap  and  also,  to  a  certain  extent,  by  the  ad- 
justment of  the  interrupter  on  the  coil.  It  can  be  varied 
from  a  very  slight  pricking  sensation  obtained  from  the 
vacuum  electrode,  to  a  light  violet  glow  in  the  same  which 
produces  a  strong  sparking  effect  between  the  glass  and 
the  skin  of  the  patient. 

The  apparatus  is  connected  direct  to  the  main  and  no 
auxiliary  resistance  or  other  apparatus  is  necessary. 


HIGH  FREQUENCY  CURRENTS 


139 


The  current  from  this  apparatus  produces  a  violet  brush 
discharge  when  the  glass  electrode  is  brought  in  close 
proximity  to  the  tissues,  the  discharge  is  produced  at  the 
outer  surface  of  the  glass  by  induction,  and  corresponds 
in  polarity  to  the  current  flowing  in  the  wire  within  the 


Fig.  68 


Invictus  portable  high  frequency  apparatus. 


glass  electrode.  There  is  a  certain  amount  of  heat  pro- 
duced which  in  these  small  currents  is  not  discernible  if 
good  conduction  is  established.  The  interiors  of  the  tubes 
are  liable  to  be  heated  slightly  by  the  incandescence  of  the 
luminous  discharges  of  the  current. 


CHAPTER  VI. 

DENTAL  ELECTRICAL  APPARATUSES  AND 
APPLIANCES. 

Motors — Electric  Engines — Electric  Lathes — Switchboards — Accumu- 
lators—Direct Resistance — Motor  Converter — Electric  Hot-air  Syringe — 
Electric  Sterilizer  and  Hot  Water  Apparatus — Footwarmer — Electric 
Furnaces — Pyrometer — Electric  Gold  Annealer. 

Motors. — Motors  for  operating  room  engines,  laboratory 
polishing  and  grinding  lathes,  ventilating  fans  and  com- 
pressed air  pumps,  are  usually  constructed  of  a  pair  of 
fixed  electro-magnets  for  generating  a  magnetic  field,  an 
armature  which  revolves  in  the  magnetic  field,  and  a  con- 
trolling resistance  for  regulating  the  speed. 

The  electric  field  magnets  are  two  separate  coils  of 
insulated  wire  wound  in  opposite  directions  and  fitted  on 
to  shaped  soft  iron  cores  or  pole  pieces.  The  armature  is 
the  driving  force  of  the  motor  and  consists  of  a  number  of 
coils  of  wire  wound  in  slotted  plates  fitted  to  the  spindle. 
The  ends  of  the  coils  terminate  at  a  commutator,  which  is 
composed  of  a  number  of  copper  segments  insulated  from 
each  other  and  from  the  steel  spindle  to  which  it  is  fixed. 
On  the  surface  of  the  commutator  a  pair  of  brushes  make 
contact  and  are  held  in  position  by  suitable  holders  and 
springs,  which  hold  the  brushes  firmly  against  the  surface 
of  the  commutator  as  the  armature  revolves.  These 
brushes  carry  the  current  supply  to  the  armature. 

The  commutator  of  all  motors  should  have  regular 
attention.  The  surface  must  be  kept  smooth  and  clean 
and  sufficient  tension  given  to  the  brush  springs  to  keep 
the  brushes  from  jumping  as  the  armature  revolves,  not 
enough,  however,   to   cause  undue  wear  between  the  sur- 


DENTAL  ELECTRICAL  APPARATUSES  141 

faces  of  the  brushes  and  the  commutator.  To  clean  the 
commutator  a  piece  of  soft  cloth  should  be  firmly  wrapped 
around  the  tip  of  the  forefinger,  moistened  with  spirit  and 
pressed  on  to  the  surface  as  the  armature  revolves.  This 
can  be  done  with  ordinary  care,  without  fear  of  shock.  The 
motor  should  then  be  stopped,  the  brushes  should  be  lifted 
and  the  contact  surfaces  carefully  wiped.  Should  the 
brushes  be  of  metal  gauze,  care  should  be  taken  not  to  fray 
the  edges,  as  frayed  edges  cause  sparking  at  the  brushes, 
which  must  be  prevented  as  much  as  possible,  because  it 
burns  the  surface  of  the  commutator  and  makes  it  uneven, 
and  may  later  on  lead  to  a  burn-out  of  the  armature.  If 
the  surface  of  the  commutator  is  at  all  rough,  or  blackened 
carbon  brushes  are  used,  a  piece  of  fine  sand  or  cuttle  fish 
paper  should  be  held  flat  on  it  as  the  armature  revolves, 
until  a  smooth  bright  surface  is  obtained.  Any  dust  on 
the  brushes  and  commutator  should  be  afterward  care- 
fully wiped  off.     Emery  paper  should  not  be  used. 

Motors  which  have  carbon  brushes  should  have  the  sur- 
faces of  all  internal  parts  wiped  clean  from  carbon  dust, 
since  if  this  is  allowed  to  deposit  it  may  in  time  cause  a 
short  circuit  and  seriously  damage  the  motor. 

The  bearings  should  be  sparingly  oiled  and  every  care 
should  be  exercised  not  to  allow  surplus  oil  to  run  over  the 
insulating  material  of  any  wires,  as  oil  destroys  it  by  its 
action  on  the  rubber. 

Careful  attention  to  the  above-mentioned  points  will 
insure  long  life  to  the  motor  and  often  save  an  expensive 
"burn-out." 

Electric  Engines. — There  are  a  number  of  electric  engines 
in  the  market,  chiefly  of  American  and  German  manu- 
facture, the  original  being  the  well-known  "Columbia," 
made  by  the  Ritter  Dental  Manufacturing  Co.,  of  Roch- 
ester, U.  S.  A.  The  motor  is  enclosed  in  two  metal  hemi- 
spheres and  hangs  by  a  circular  cord  from  a  suitable  wall 
bracket  with  pulleys,  and  is  about  ^  horse  power.  The  sus- 
pension cord  consists  of  four  feed  wires,  two  for  the  field 
magnets  and   two  for  the  armature.     These  are   twisted 


142  ELECTRO-PHYSICS 

together  and  covered  with  insulating  cotton  and  silk,  built 
into  a  neat  circular  form.  The  cord  passes  over  the  two 
pulleys  and  down  the  wall  on  which  the  bracket  is  fixed, 
and  has  attached  to  it  a  lead  weight  to  counter-balance 
the  motor  and  to  admit  of  it  being  raised  or  lowered  with 
a  light  touch  of  the  operator's  hand.  The  cord  finishes 
at  a  small  contact  plate  or  resistance  box  which  is  fixed 
to  the  wall,  usually  from  one  to  two  feet  from  the  floor, 
and  fitted  with  a  pair  of  terminals  for  connecting  the  engine 
to  the  electric  supply  mains,  by  means  of  ordinary  twin 
flexible  wire;  it  also  acts  as  a  connecting  plate  for  the  ends 
of  the  floor  cable  which  leads  from  the  foot  controller. 
This  cable  contains  four  to  eight  separate  wires. 

The  resistance  usually  consists  of  a  number  of  coils  of 
wire,  wound  on  some  suitable  insulating  material  and 
enclosed  in  a  separate  box  or  in  the  foot  controller.  These 
coils  have  wires  which  lead  to  copper  contacts  in  the  con- 
troller, over  which  pass  spring  contacts,  worked  by  means 
of  a  foot  lever.  The  contacts  control  the  entire  working 
of  the  motor — starting,  stopping,  speed-regulation,  etc. 

The  controlling  lever  of  the  foot  switch  generally  has  a 
free  swinging  movement  and  requires  to  be  held  in  position 
with  the  operator's  foot  while  the  motor  is  in  action.  Some 
manufacturers  fit  a  locking  device  which  holds  the  lever 
in  any  desired  position  and  is  released  by  a  slight  tap  with 
the  foot.  The  locking  device  is  not  so  safe  as  the  free 
lever,  since,  should  it  be  necessary  to  stop  a  revolving 
burr  instantaneously,  some  few  seconds  may  be  lost  in  the 
effort  to  release  the  controlling  lever,  whereas  with  the 
free  swinging  lever  the  operator  instinctively  withdraws 
his  foot  and  the  motor  immediately  stops. 

Foot  controllers  should  be  opened  occasionally  and 
carefully  cleaned,  especially  the  surfaces  of  the  various 
contacts.  After  cleaning,  the  surfaces  should  be  smeared 
with  a  very  slight  film  of  oil,  to  prevent  wear  of  the  two 
copper  surfaces  by  friction.  Too  much  grease  will  cause 
loss  of  power  in  the  motor,  because,  being  an  insulator,  it 
interferes  with  passing  of  current. 


DENTAL  ELECTRICAL  APPARATUSES  143 

Other  designs  of  engines  found  in  catalogues  of  the  dental 
manufacturers  and  supply  houses  are  all  practically  con- 
structed as  described  above  with  various  modifications, 
chiefly  in  the  controller;  some  are  fitted  with  the  flexible 
cable,  and  others  with  the  all-cord  arm  for  receiving  the 
hand-piece  and  instruments. 

The  all-cord  arm  is  superseding  the  flexible  cable  arm  to 
a  very  large  extent,  although  the  cable  arm  possesses  the 
advantage  of  adaptability,  particularly  in  the  wrist,  and  this, 
from  the  operator's  point  of  view,  is  a  great  convenience. 

Electric  Lathes. — These  are  more  simple  than  engines  for 
operating  rooms,  and  usually  consist  of  a  motor,  which 
varies  from  -^  to  \  horse  power  with  suitable  spindles. 
The  motor  case  is  completely  closed,  ventilation  holes  not 
being  necessary,  as  these  lathes  are  not,  as  a  rule,  run  for 
long  periods,  and,  therefore,  do  not  generate  much  heat  in 
the  coils,  and  it  is  also  important  that  grit  and  moisture 
from  the  polishing  brushes  and  grinding  wheels  be  excluded 
from  the  working  parts.  The  armature  spindle  extends 
on  each  side  of  the  motor  beyond  the  bearings  for  about 
an  inch,  and  on  these  ends  the  chucks  are  fixed,  they 
are  very  slightly  tapered,  while  the  chucks  are  correspond- 
ingly tapered.  Chucks  fitted  in  this  manner  are  held  very 
securely  on  the  spindle,  and  can  only  be  removed  by  direct 
pressure  along  the  spindle,  such  pressure  being  usually  applied 
to  the  outside  of  the  bearings. 

Switchboards. — Various  forms  of  switchboards  have  been 
specially  designed  and  manufactured  for  dentists'  use. 
These  provide  methods  for  supplying  and  controlling  both 
high  and  low  voltages  by  means  of  suitable  switches,  safety 
"  cut-outs,"  regulating  rheostats,  etc. 

The  modern  switchboards  are  usually  made  up  in  panel 
form  arranged  for  attachment  to  the  wall  or  cabinet,  within 
easy  reach  of  the  operator  from  the  chair  side.  The  panel 
is  generally  either  of  marble  or  enamelled  slate  fitted  to  a 
metal  frame,  and  contains  the  necessary  connections,  wire 
resistances,  etc. 

The  high  voltage  circuit,  as  a  rule,  has  four  or  six  terminals 


144  ELECTRO-PHYSICS 

to  which  flexible  wires  can  be  attached  for  the  engine, 
lathe,  fan,  gold  annealer,  reflector,  sterilizer,  hot-water 
apparatus,  etc.,  or  to  any  appliance  which  is  made  to  work 
with  the  same  electro-motive  force  as  is  possessed  by  the 
particular  current  supply  available.  Each  terminal  is 
controlled  by  a  quick  break-switch,  and  a  "cut-out,"  and 
the  operator  can  switch  the  current  on  to  or  off  from  any 
of  these  appliances,  without  moving  from  the  chair-side. 
It  is  important  that  the  fuse  wires  in  cut-outs  should  be  of 
the  correct  size  to  carry  the  amperes  required  by  each 
apparatus;  heavy  fuses  for  low  amperage  appliances  are 
practically  useless.  Fuses  are  intended  for  the  purpose  of 
protecting  the  appliances  in  use  and  preventing  them 
being  burned  out  or  injured  by  a  sudden  rush  of  current, 
due  to  some  defect  or  short  circuit. 

The  approximate  sizes  of  fuse  wires  required  for  high 
voltages  200  to  250  volts  are  as  follows: 

For  motor,  engine,  lathe,  fan,  reflector,  etc.,  1  ampere. 

For  Mitchell's  low-fusing  inlay  furnace,  annealer,  ato- 
mizer and  tumbler  heater,  2  amperes. 

For  high  fusing  inlay  furnace,  sterilizer,  and  hot-water 
apparatus,  3  to  5  amperes. 

All  high  voltage  terminals  should  be  designed  so  that  it 
is  practically  impossible  for  the  operator  to  short-circuit 
them  accidentally  or  to  receive  a  shock. 

Low  voltage  circuit  is  required  for  such  appliances  as 
cannot  be  used  from  the  full  voltage  of  the  current  supply, 
as,  for  example,  mouth  examining  and  antrum  lamps,  root- 
drier,  cautery,  gutta-percha  heating  instruments,  hot-air 
syringe,  etc.  These  usually  require  a  current  of  from  2 
to  12  volts,  and  from  §  ampere  to  8  amperes. 

When  the  current  is  alternating,  the  low  voltage  circuit 
is  easily  attainable  from  a  suitable  design  of  transformer, 
fitted  either  on  the  front  or  back  of  the  switchboard  panel. 
This  circuit  consists  of  primary  and  secondary  coils  wound 
on  a  soft  iron  core  of  convenient  shape,  and  a  regulating 
rheostat  for  graduating  the  voltage  and  amperage  in  regular 
and  gradually  increasing  ratio.     The  low  voltage  current 


DEXTAL  ELECTRICAL  APPARATUSES  145 

used  is  taken  from  the  secondary  coil  which  is  quite  separate 
from  the  main  current  supply. 

When  the  current  is  continuous,  especially  if  it  be  of 
high  E.  M.  F.  (200  to  250  volts),  the  difficulty  in  reducing 
the  E.  M.  F.  to  2,  4,  6  volts,  etc.,  and  at  the  same 
time  obtaining  a  graduated  amperage  at  these  low  volt- 
ages, is  very  much  greater,  and  represents  a  heavier  loss  of 
current  than  when  the  current  is  alternating.  There  are 
various  methods  employed  for  this  purpose.  The  three 
most  practicable  are  those  used  by  the  various  manu- 
facturers, viz.,  accumulators,  direct  resistance,  and  the 
motor  converter. 

Accumulators. — A  two-cell  accumulator  which  gives  a 
little  over  4  volts  when  fully  charged,  is  connected  to 
a  pair  of  terminals  on  the  lower  part  of  the  switchboard. 
By  means  of  wires  behind  the  board  the  cells  are  connected 
to  a  resistance  coil  with  a  sliding  contact,  which  is  con- 
nected to  three  or  four  terminals  on  the  edge  of  the  board. 
The  flexible  wires  for  the  mouth  lamp,  cautery  syringe, 
etc.,  are  connected  to  these  terminals.  All  these  instru- 
ments are  constructed  to  work  on  from  2  or  4  volts. 
The  current  from  the  cells  passes  through  the  resistance 
and  by  slowly  moving  the  sliding  contact  from  one  end  of 
the  resistance  toward  the  other,  the  current  can  be  very 
gradually  increased  until  the  correct  strength  is  obtained 
to  light  the  lamp  or  heat  the  instrument  required  for  use. 

The  cells  are  usually  charged  through  high  candle  power 
lamps  fitted  on  the  upper  part  of  the  board,  which  act  as  a 
resistance  to  the  high  voltage  of  the  current  supply.  The 
lamps  should  be  of  the  same  voltage  as  the  lighting  or 
power  current  used.  The  lamps  are  switched  into  the 
accumulator  circuit  by  means  of  a  double  pole-switch,  so 
that  when  the  current  is  being  taken  from  the  cells  the 
high  voltage  supply  can  be  disconnected;  this  prevents  the 
possibility  of  either  operator  or  patient  receiving  a  shock, 
which  might  happen  if  a  single  pole-switch  is  used. 

A  volt-meter  is  useful  for  detecting  the  lowering  of  the 
power  in  the  cells;  it  is  most  important  to  keep  these  fully 
10 


146  ELECTRO-PHYSICS 

charged,  if  the  E.  M.  F.  is  allowed  to  drop  below  2  volts, 
the  acid  in  the  cells  acts  on  the  plates  and  quickly  destroys 
them. 

Accumulators  are  very  satisfactory  so  long  as  they  are 
carefully  watched  and  kept  charged,  but  operators  are 
liable  to  forget  them,  and  when  the  cells  begin  to  go  wrong, 
owing  to  neglect,  they  become  a  source  of  trouble.  A 
disadvantage  connected  with  accumulators  is  the  glare 
from  the  lamps  which  have  to  burn  for  long  intervals  during 
recharging. 

Direct  Resistance. — In  this  form  of  resistance  the  back 
of  the  switchboard  is  fitted  with  coils  of  resistance  wire,  or 
other  resistance  material  in  the  form  of  metal  plates,  the 
wire  being  of  the  correct  gauge  and  length  to  reduce  the 
high  voltage  supply  to  2  volts  and  a  fraction  of  an  am- 
pere. For  voltages  of  from  200  to  250  volts,  coils  of  thick 
iron  wire  of  considerable  length,  with  ample  air  space,  are 
attached  to  the  back  of  the  slate  slab.  The  current  in  pass- 
ing through  the  wire  resistance  generates  considerable  heat 
which  is  dissipated  in  the  ventilation  spaces  provided. 

At  regular  distances  along  the  main  resistance,  short 
wires  are  attached  and  connected  to  a  series  of  studs  on 
the  switchboard — some  thrity  or  more  in  number.  A 
sliding  contact  passes  over  these  studs  and  reduces  a  por- 
tion of  the  resistance  at  each  step,  thereby  gradually  in- 
creasing the  strength  of  the  current  to  the  terminals  which 
are  connected  to  the  circuit  for  the  use  of  the  cautery, 
syringe,  root-drier,  etc.  As  the  resistance  is  reduced  the 
amperage  rises  in  proportion,  and  also  the  temperature  of 
the  wire.  They  are  at  their  maximum  when  the  cautery 
is  in  use;  this  instrument  generally  requires  a  current  of 
from  6  to  8  amperes  and  E.  M.  F.  of  2  to  4  volts. 

Where  a  cautery  is  used  from  voltages  of  200  volts  and 
upward,  it  is  often  considered  advisable  to  fit  the  heavier 
resistance  wire  into  a  separate  frame,  suitable  for  standing 
on  the  floor,  in  order  to  reduce  the  heat  given  off  at  the 
back  of  the  board. 

This  arrangement  is  not  dangerous  or  as  wasteful  as  may 


DENTAL  ELECTRICAL  APPARATUSES  147 

be  imagined,  for  these  low  voltage  appliances  are,  as  a  rule, 
only  required  occasionally  during  an  average  day's  practice, 
and  then  only  for  very  short  intervals,  probably  only  for 
two  or  three  minutes  at  a  time,  it  will  readily  be  seen  that 
the  current  is  not  passing  through  the  resistance  long 
enough  to  produce  much  heat  or  to  waste  any  great  quantity 
of  current.  With  ordinary  care  no  trouble  may  be  antici- 
pated, but  it  is  advisable  to  have  a  lamp  fitted  on  the  board 
to  act  as  a  signal.  This  lamp  only  lights  when  the  resist- 
ance circuit  is  in  use;  the  light  will  then  always  warn  the 
operator  that  the  current  is  still  passing,  should  he  forget 
to  switch  off  the  resistance  after  using  the  cautery,  syringe, 
etc. 

With  the  direct  resistance  method  one  pole  of  the  main 
supply  is  always  connected  to  the  low  voltage  terminals, 
hence  it  is  possible  to  receive  a  shock  if  the  handles  of  the 
appliances  used  are  not  perfectly  insulated.  The  advantage 
of  the  method  is  that  so  long  as  the  main  current  is  avail- 
able the  supply  is  always  certain,  and  the  operator  is  saved 
the  necessity  of  constantly  watching  the  apparatus,  as  is 
necessary  when  accumulators,  (which  require  regular  charg- 
ing), are  used. 

The  Motor  Converter. — An  alternating  current  is  the  most 
satisfactory  for  producing  low  voltages;  when  a  fairly 
heavy  amperage  is  required  it  is  readily  transformed  with 
very  little  current  loss  or  heat  and  with  absolutely  no  risks 
of  shock  from  the  high  voltage  circuit. 

When  a  continuous  current  has  to  be  used,  the  safest 
and  best  method  of  producing  the  low  voltage  current  is  by 
means  of  a  motor  converter.  This  consists  of  an  ordinary 
continuous  current  motor  with  alternating  current  collect- 
ing rings  and  brushes  fitted  to  the  armature  at  the  end 
opposite  to  the  commutator.  This  combination  when  run 
by  the  continuous  current  acts  both  as  a  motor  and  a 
dynamo,  an  alternating  current  is  given  off  from  the  collect- 
ing rings  of  the  armature,  which  is  conducted  by  a  pair  of 
wires  to  a  primary  coil  of  a  small  transformer  fitted  to  the 
switchboard.     This  produces  a  low  voltage  current  which 


148  ELECTRO-PHYSICS 

passes  through  the  secondary  coil  of  the  transformer,  from 
which  it  is  conveyed  by  means  of  a  sliding  contact.  A 
graduated  current  is  by  this  means  obtained  to  suit  volt- 
age  and   amperage    of   the   various   instruments. 

The  only  disadvantage  of  the  motor  converter  method  is 
that  a  small  motor  is  necessary,  in  addition  to  the  switch- 
board, but  all  trouble  of  attending  to  accumulators,  the 
need  of  heavy  resistance  coils,  and  the  unavoidable  heating 
are  done  away  with;  moreover,  all  risk  of  shocks  to  either 
patient  or  operator  is  entirely  avoided. 

If  desired,  the  motor  can  be  put  out  of  the  way  in  a 
box  or  cupboard,  or  it  may  be  placed  in  another  room  and 
controlled  by  a  switch  on  the  switchboard.  In  addition  to 
the  special  work  for  which  it  is  intended  it  can  also  be  used 
in  the  operating  room  as  a  lathe,  when  not  employed  for 
generating  the  low  voltage  current. 

By  this  method  the  low  voltage  circuit  only  is  converted 
to  alternating  current;  the  high  voltage  continuous  current 
circuit  remains  unaffected  and  always  available  for  motors 
and  heating  apparatuses. 

A  modern  switchboard  is  shown  in  Fig.  69.  This  is  sup- 
plied either  with  the  direct  resistance  or  with  the  motor 
converter.  When  the  motor  converter  is  employed  the 
motor  is  fitted  up  for  use  as  an  operating  room  lathe  and 
thus   answers   a   double   purpose. 

Low  voltage  instruments  may  be  used  with  switch- 
boards or  accumulators  when  they  are  provided  with 
suitable  means  for  controlling  and  regulating  the  current 
supply. 

These  instruments,  as  a  general  rule,  require  an  electro- 
motive force  of  from  2  to  10  volts,  and  an  amperage  of  from 
|  ampere  to  8  amperes. 

Most  switchboards  provide  for  the  safe  use  of  instru- 
ments of  this  class,  but  they  can  also  be  worked  from  any 
of  the  ordinary  commercial  accumulators,  provided  a  suit- 
able regulating  resistance  is  employed  to  prevent  an  undue 
rush  of  current. 

One  of  the  most  complete  sets  of  low  voltage  instruments 


Fia.  r>9 


Switchboard. 


150 


ELECTRO-PHYSICS 


is  the  Russel  set,  made  by  the  Electro  Dental  Manufactur- 
ing Co.,  and  comprises  mouth  and  antrum  examining  lamps, 
root-drier,  gutta-percha  and  wax  heating  instruments, 
cautery,  and  bleaching  points. 

The  lamps  are  made  for  use  at  4,  6,  8,  and  10  volts.  The 
cautery  which  has  a  platinum  loop  is  heated  to  a  bright 
red  with  a  current  of  from  3  to  4  volts,  and  6  to  8  amperes. 
The  root-drier  and  other  heating  points  consist  of  thin 
silver  or  copper  tubes  which  terminate  in  solid  shaped  ends; 


Fig.  70 


Mouth  lamp  from  main. 

inside  the  tubes  for  about  two-thirds  of  the  length  of  the 
instrument,  a  fine  platinum  loop  is  inserted,  this  loop 
requires  to  be  heated  with  care  as  the  effect  of  the  current 
upon  it  is  not  visible,  as  it  is  upon  the  bare  loop  of  the 
cautery.  The  heat  generated  in  the  loop  travels  to  the 
point  and  the  temperature  is  regulated  by  the  resistance 
already  mentioned.  These  points  require  from  2  to  4  volts 
and  1  to  2  amperes. 

The  root-drier  has  a  very  fine  flexible  point  which  readily 
dries  any  moisture  in  a  .root  canal  in  which  it  is  inserted. 


DENTAL  ELECTRICAL  APPARATUSES  151 

Gutta-percha  stoppings  are  readily  trimmed  and  packed 
with  points  for  that  purpose,  after  the  temperature  has 
first  been  adjusted  to  the  proper  degree. 

The  electric  mouth  lamp  with  mirror  used  for  many 
purposes  is  valuable  for  careful  examination  of  the  mouth. 
The  powerful  light  reveals  dead  teeth  and  fissures  which 
may  be  overlooked  when  the  mouth  is  examined  without 
the   lamp. 

This  lamp  can  be  used  with  the  current  from  small  dry 
batteries  or  accumulators,  and  also  in  series  with  an  ordin- 
ary low  candle-power  lamp  or  permanent  resistance. 

The  mouth  lamp  with  a  permanent  resistance,  which 
can  be  used  from  any  ordinary  lighting  circuit,  is  shown  in 
Fig.  70. 

Electric  Hot-air  Syringe. — This  usually  consists  of  a 
platinum  coil  fitted  inside  a  glass  tube,  protected  by  a 
metal  sheath  which  is  perforated,  to  admit  of  the  coil  being 
seen,  so  that  the  current  can  be  adjusted  to  produce  the 
proper  degree  of  heat.  The  syringe  is  adapted  for  use  with 
compressed  air.  The  electric  current  and  air  supply  are 
switched  on  or  off  by  a  single  movement  of  the  switch 
which  is  fitted  in  the  handle.  The  current  required  for 
working  it  is  6  volts  and  from  4  to  6  amperes. 

A  syringe  is  made  which  can  be  worked  without  any 
resistance  direct  from  any  current  of  high  electro-motive 
force.  A  separate  switch  with  a  valve  controls  the  current 
and  air  supply.  The  current  which  is  only  in  circuit  for 
about  half  a  minute  at  a  time,  generates  sufficient  heat  in 
the  coil  for  three  or  four  minutes'  use. 

Electric  Sterilizers  and  Hot-water  Apparatus. — A  form  of 
sterilizer  consists  of  a  water  container  made  of  brass  which 
is  pressed  from  one  piece,  it  has  therefore  no  seams  or 
soldered  joints.  The  heating  element  is  composed  of  a 
special  alloy,  made  into  a  flat  wire  which  is  wound  on  an 
iron  plate  insulated  with  mica.  Two  of  these  elements  are 
fitted  in  the  bottom  of  the  water  container  to  which  they 
are  firmly  clamped  and  connected  with  wires  to  three 
terminals  which  are  fixed  to  the  base.     Connectors  pro- 


152  ELECTRO-PHYSICS 

vided  with  triple  flexible  wires  admit  of  four  different 
temperatures  being  obtained. 

The  sterilizer  is  so  designed  that,  in  case  of  an  accidental 
fusing  of  one  or  both  of  the  heating  elements,  the  base  can 
readily  be  removed,  the  elements  taken  out  and  repaired 
or  replaced  by  new  ones. 

In  using  a  sterilizer  care  must  be  exercised  to  ensure 
that  the  water  is  not  allowed  to  boil  completely  away  and 
leave  the  container  dry.  Should  the  container  become  dry 
the  heating  elements  will  be  over-heated  and  destroyed. 
This  precaution  is  necessary  with  all  forms  of  hot  water 
jugs,  kettles,  sterilizers,  etc. 

A  form  of  sterilizer,  of  American  manufacture,  known 
as  the  "Monarch"  Visible  Sterilizer,  is  made  of  cast  alumi- 
nium which  is  strong,  light,  and  easily  cleaned,  the  glass 
vessel  is  made  of  specially  annealed  triple  lead  glass  which 
the  manufacturers  claim  will  not  crack  with  ordinary  use. 
The  heater  is  in  the  form  of  an  immersion  element  made  of 
cast  brass,  in  which  a  special  form  of  wire  is  fitted,  wound, 
and  insulated  in  such  a  way  that  it  will  stand  constant 
use  without  risk  of  fusing,  provided  the  current  is  not 
switched  on  except  when  the  element  is  in  the  water.  When 
not  used  for  sterilizing  purposes  the  glass  vessel  can  be 
employed  as  a  heater  for  the  atomizer 'bottles. 

Many  forms  of  electrical  jugs,  kettles,  and  tanks  are  now 
made  for  heating  and  boiling  water  in  the  operating  room, 
which  are  constructed  on  the  principle  described. 

Foot  Warmer. — The  foot  warmer  consists  of  a  thin  metal 
case  which  encloses  a  wire  resistance  that  is  designed  not 
to  reach  a  high  temperature,  even  though  the  current  be 
left  on  for  an  hour  or  more  at  a  time.  It  is  covered  with 
carpet  which  gives  it  a  neat  appearance  while  the  heat 
generated  is  just  comfortable  to  the  feet. 

Electrical  Furnaces. — Electric  furnaces  consist  of  fire- 
clay muffles  wound  with  platinum  or  iridio-platinum  wire, 
no  other  metal  or  alloy  having  as  yet  been  found  which 
will  stand  the  high  temperatures  necessary  for  fusing 
mineral  or  porcelain  bodies.    Even  with  platinum  or  iridio- 


DENTAL  ELECTRICAL  APPARATUSES 


153 


platinum  wire  it  is  practically  impossible  to  prevent  "  burn- 
outs," which  are  mainly  due  to  overheating,  or  to  the  too 
sudden  switching  on  or  off  of  high  electro-motive  force. 

The  wire  around  muffles  should  be  laid  in  grooves  and 
wound  on  the  outer  surface  to  prevent  the  coils  coming  in 
contact  with  each  other  during  expansion,  contact  causes 
a  short  circuit  and  fusing  of  the  wire. 

Fig.  71 


Pelton  electrical  furnace. 


The  wire  necessary  for  wiring  a  muffle  varies  in  diameter 
and  length  according  to  the  voltage  of  the  current  to  be 
used  and  the  temperature  required.  Very  accurate  cal- 
culations are  necessary  to  determine  these  points  and  to 
ensure  correct  resistance  to  heat  the  wire  to  the  right  tem- 
perature without  overheating,  or,  on  the  other  hand,  not 
heat  the  furnace  sufficient  to  fuse  mineral  or  porcelain 
bodies. 


154 


ELECTRO-PH  YSICS 


DENTAL  ELECTRICAL  APPARATUSES  155 

Pyrometer. — The  pyrometer  is  intended  for  use  with  the 
electric  furnace.  It  is  connected  to  the  muffle  by  means  of 
a  thermocouple,  which  registers  the  temperature  generated 
in  the  muffle.  If  the  fusing  point  of  the  metal  or  porcelain 
body  is  known,  it  can  be  fused  without  opening  the  muffle 
door,  by  simply  watching  the  needle  of  the  pryometer  and 
reducing  the  current  in  the  muffle  as  soon  as  the  required 
temperature    is    registered. 

The  pyrometer  is  a  very  delicate  instrument  and  some- 
what expensive.  It  works  independently  of  the  ordinary 
electric  current  supply  and  develops  a  thermal-electric 
current  in  its  own  current.  The  thermo-couple  consists 
of  two  pieces  of  wire,  platinum,  and  iridium,  which  are 
insulated  from  each  other,  except  at  their  extreme  ends. 
Two  of  the  ends  are  fused  together  while  the  other  two  have 
flexible  wires  attached  for  connecting  them  to  the  terminals 
of  the  pyrometer.  The  fused  part  is  fitted  into  the  furnace 
muffle  and  the  action  of  the  heat  generates  the  thermal 
current  which  passes  along  the  flexible  wires  and  acts  on 
a  small  coil  in  the  pyrometer  which  acts  on  the  needle. 

Electric  Gold  Annealer. — The  electric  annealer  is  con- 
structed of  a  fire-clay  slab  of  about  three  inches  square, 
divided  into  sections,  wired  underneath  with  platinum 
wire,  and  fitted  to  a  small  stand  which  has  a  metal  cover. 
Pelton's  annealer  is  fitted  with  a  regulating  resistance  which 
allows  of  varying  temperature  being  obtained. 


CHAPTER  VII. 
THE  X-RAYS  OR  RONTGEN  RAYS.1 

X-rays  Apparatus — Technique  of  Dental  Radiography — X-ray  Diagnosis. 

The  Rbntgen  Rays  Apparatus.1 — A"-rays  are  produced  by 
passing  an  electric  spark,  usually  from  10  to  18  inches  long 
in  air,  from  an  induction  coil  or  other  electric  machine, 
through  a  special  glass  tube  having  a  high  vacuum,  and 
enclosing  terminals  known  as  the  cathode  and  the  anti- 
cathode,  which  latter  is  frequently  joined  to  another  called 
the  anode. 

Cathode  rays  are  thus  produced  in  the  tube,  which  striking 
a  target  (anticathode)  made  of  metal  of  high  atomic  weight 
and  fusing  point,  give  off  the  x-rays  in  the  tube,  which  pene- 
trate the  glass  sides  of  the  tube  on  the  same  side  as  that 
of  the  anticathode  struck  by  the  cathode  stream. 

X-rays  thus  produced  in  the  air  have  the  power  of  pene- 
trating all  substances  more  or  less,  according  to  their 
strength,  and  also  in  the  same  ratio  as  the  atomic  weight 
or  density  of  those  substances.  They  also  have  the  power 
to  fluoresce  certain  substances,  as  barium-platino  cyanide, 
potassium  platino-cyanide,  tungstate  of  calcium,  etc.  The 
x-rays  also  affect  photographic  plates  of  all  kinds  more  or 
less,  according  to  the  thickness  and  quality  of  the  emulsion, 
the  effect  being  produced  in  all  probability  by  bombardment 
of  the  x-rays  particles. 

Special  x-ray  plates  are  made  and  at  the  present  time 
the  Ilford  are  the  best.  Of  the  photographic  varieties,  the 
"ordinary"  speed  are  usually  better  than  the  "rapid,"  but 
again  the  writer  has  obtained  excellent  results  from  such 

1  By  Mr.  Charles  A.  Clark,  of  London. 


THE  X-RAYS  OR  RON T GEN  RAYS  157 

fast  emulsions  as  Paget  5X  Luniiere's  Sigma,  and  Extra 
Rapid,  though  all  of  these  require  a  longer  exposure  than 
the  special  .T-ray  plates  mentioned. 

At  the  present  time  for  obtaining  the  current  for  the 
x-rays  the  coil  is  the  most  usual  instrument.  At  first  these 
were  made  to  give  a  spark  of  a  certain  length  only,  but  now 
the  great  aim  is  to  obtain  not  only  length  of  spark  but  as 
large  a  current  as  possible.  Different  makers  have  different 
methods  of  building  coils,  and  a  general  description  only  will 
therefore  be  given. 

The  coil  consists  essentially  of  (1)  an  iron  core;  (2) 
primary  winding,  and  (3)  secondary;  between  these  two 
latter  there  is  a  thick  ebonite  tube.  In  the  early  days  the 
iron  core  was  made  rather  too  small;  it  is  now  made  of 
bundles  of  thin  soft  iron  wire  or  of  soft  iron  laminae. 

Outside  this  core  is  the  primary  (duly  insulated  from 
the  core)  of  thick  double  cotton  covered  copper  wire. 
Originally  this  was  made  in  two  layers,  the  wire  being 
wound  to  the  end  and  then  back  again  on  the  first  layer. 
Now  it  is  made  in  six  or  more  parallels,  to  which  the 
primary  current  can  be  adjusted. 

The  whole  of  the  primary  and  the  core  are  placed  in  the 
ebonite  tube,  which  is  filled  up  with  an  insulating  medium, 
usually  hard  paraffin. 

Outside  this  is  the  secondary  winding  of  thin  double 
silk-covered  wire.  This  wire  is  of  increasing  thickness  toward 
each  end  of  the  coil,  so  as  to  obtain  as  much  current  as 
possible. 

Some  make  this  secondary  in  vertical  sections  of  |  inch 
thick  to  build  up  the  coil.  One  maker  makes  this  secondary 
sectionless,  that  is,  only  one  layer  of  wire  between  sheets 
of  paraffin  paper.  This  has  to  be  wound  in  a  horizontal 
position,  a  small  roller  preventing  the  wire  overlaying.  An- 
other maker  winds  the  secondary  from  end  to  end,  always 
keeping  to  the  proper  number  of  turns  and  over  each  layer 
of  wire,  sheets  of  insulated  paper  are  laid.  Over  all  is  laid  a 
thin  sheet  of  ebonite,  and  the  ends  of  the  coil  covered  with 
thick  ebonite  disks. 


158  ELECTRO-PHYSICS 

Coils  are  made  to  suit  the  voltage  that  is  to  be  used, 
usually  from  the  main  up  to  250  volts.  They  can  also  be 
made  for  as  low  a  voltage  as  20  volts,  but  probably  the 
most  suitable  is  100  volts. 

The  current  is  direct  but  interrupted,  and  its  action  is 
to  produce  a  secondary  current  at  a  very  high  potential; 
but  compared  with  the  amperage  of  the  primary,  of  a  very 
small  milliamperage,  this  latter  being  from  \  milliampere 
up  to  25  or  30  milliamperes,  which  would  be  considered  a 
heavy  secondary  discharge. 

A  condenser  made  of  sheets  of  tin-foil  separated  by  a 
dielectric  is  necessary  to  obtain  the  required  length  of 
spark  and  current,  except  when  the  electrolytic  break  is 
used,  when  it  is  "cut  out."  The  action  is  to  take  up  cur- 
rent produced  at  the  "make"  of  the  interrupter  so  that  it 
is  discharged  at  the  "break"  of  the  interrupter,  thus  greatly 
increasing  the  spark,  as  the  current  produced  at  the  break- 
ing of  contact  is  the  one  desired.  So  that  when  the  inter- 
rupter "makes"  a  current  flow  in  one  direction,  but  on 
breaking  it  flows  in  the  contrary  direction  and  a  surging 
current  is  therefore  set  up. 

At  the  present  time  coils  are  made  of  such  power  that  it 
is  possible  to  obtain  perfect  radiographs  by  means  of  a 
single  flash  with  the  aid  of  an  intensifying  screen;  such  are 
the  Dessauer  Coil  and  Siemens. 

The  Dessauer  consists  of  a  very  large  coil,  the  whole  of 
which  is  immersed  in  oil  as  an  insulator.  No  interrupter 
is  required,  but  a  fuse  fitted  in  a  cartridge  is  in  circuit 
with  the  primary.  On  switching  on  the  current  (about  80 
amperes)  the  fuse  (the  thickness  of  which  is  properly  gauged) 
bursts,  and  to  prevent  arcing,  is  damped  down.  Hence  a 
"breaking"  spark  is  obtained.  The  weight  of  this  apparatus 
is  about  half  a  ton. 

The  Siemens  single  flash  apparatus  is  a  very  large  coil 
and  the  primary  current  is  gradually  let  in  and  when  at  its 
maximum  is  suddenly  broken,  the  spark  (to  prevent  arcing) 
being  blown  out  by  compressed  air.  The  advantage  of  a 
single  flash  must  be  obvious.     The  rapidity  is  such  that 


THE  X-RAYS  OR  RONTGEN  RAYS 


159 


there  is  no  blurring  through  movement,  and  also  the  anti- 
cathode  being  struck  only  once,  instead  of  many  times 
and  never  in  the  same  identical  spot  makes  for  perfect 
definition. 


Fig.  73 


te^    a*»ne 


The  "Snook"  Rontgen  apparatus. 


But  the  Snook  Rontgen  apparatus  is  an  entirely  new 
departure  and  consists  of  a  high  tension  transformer,  the 
alternating  current  of  which  is  rectified  by  a  high  tension 
commutator  or  reversing  switch  driven  by  the  rotary 
converter  which,  if  running  from  a  continuous  main,  con- 


160  ELECTRO-PHYSICS 

verts  the  current  from  continuous  to  alternating.  The 
practical  result  is  a  unidirectional  current  which  is  ideal  for 
working,  preventing  gray  negatives  and  also  preserving  the 
condition  of  the  .T-ray  tube.  It  is  also  possible  by  means 
of  a  switch  to  obtain  any  desired  current  from  1  milliampere 
to  60  milliamperes. 

The  Wimshurst  Influence  Machine  consists  of  one  or 
more  pairs  of  glass  (covered  with  a  varnish  of  shellac)  or 
ebonite  plates  on  a  single  axle.  In  each  pair  the  plates 
revolve  in  opposite  directions  and  may  be  supplied  with 
sectors  or  without.  This  machine  gives  a  comparatively 
long  spark,  according  to  its  size,  with  a  very  small  amount 
of  current  so  that  the  Wimshurst  is  termed  a  static  machine, 
but  in  America  there  are  some  Wimshurst's  built  on  a 
vertical  axle  which  will  give  as  much  as  15  milliamperes. 
The  use  of  static  machines  in  this  country  is  not  wholly 
satisfactory  owing  to  the  humidity  of  the  climate.  To 
overcome  this  they  are  sometimes  placed  in  glass  cases, 
but  then  again  these  have  their  disadvantages.  The  static 
machine  with  all  its  faults  has  advantages  over  coils  in 
that  (while  running)  the  current  is  absolutely  unidirectional; 
is  excellent  for  radioscopic  work  and — probably  owing  to 
the  small  amount  of  current — does  not  produce  a;-ray 
dermatitis.  It  is,  however,  of  little  use  for  radiographic 
work  owing  to  the  length  of  exposure. 

Static  currents  possess  therapeutic  value  in  some  cases. 

Primary  Current. — This  is  now  usually  obtained  from 
the  main  chiefly  for  these  reasons:  convenience,  increased 
voltage,  and  quantity  of  current-accumulators  requiring 
so  much  attention  as  well  as  being  an  expense. 

The  supply  from  the  main  may  be,  however,  continuous  or 
alternating,  and  if  the  latter  it  must  be  rectified,  i.  e.,  made 
continuous. 

Continuous  current  in  different  parts  of  the  country, 
unfortunately,  may  be  supplied  in  various  voltages.  Also 
it  is  generated  in  some  districts  at  as  high  voltage  as 
480  volts,  which  is  reduced  for  lighting  and  other  purposes 
in  mains  of  240  volts  by  means  of  the  three-wire  system. 


THE  X-RAYS  OR  RONTGEN  RAYS 


161 


This  consists  of  having  between  the  positive  and  negative 
wires  a  neutral  wire,  as  shown  by  the  following  diagram. 


Fig.  74 


Diagram  of  three-wire  system. 


Now  if  current  is  taken  from  the  mains  A  and  B  the  volt- 
age will  be  480.  But  if  a  neutral  main  wire  C  is  used  (elec- 
trically) between  .1  and  B,  and  connections  made  between 
A  C  and  B  C  then  will  the  current  between  A  C  and  B  C  be 
reduced  one-half — 240  volts.  It  is  also  necessary  that  an 
equal  current  is  available  on  both  sides  when  a  large  and 
sudden  demand  is  made,  as  in  switching  on  20  or  30  amperes. 
Alternating  current  must  be  rectified,  and  probably  the 
most  satisfactory  method  is  by  means  of  a  motor  gener- 
ator, which  consists  of  an  alternating  motor  of  the  voltage 
of  the  main  coupled  to  a  continuous  current  dynamo  of 
the  requisite  voltage  and  output  in  current. 
11 


162  ELECTRO-PHYSICS 

These  are  made  so  that  the  sudden  switching  on  of  a 
large  current  to  the  coil  is  possible. 

A  very  efficient  rectifier  is  the  Nodon  valve,  and  it  is 
possible  to  work  a  coil  with  it,  but  it  is  not  so  good  as  the 
above.  It  is  made  of  an  aluminium  rod  and  a  sheet  of  iron 
immersed  in  a  solution  of  phos.  sodii.  This  allows  current 
to  pass  in  one  direction  only,  the  reverse  being  dissipated 
in  the  solution  as  heat. 

If  current  from  the  main  is  not  obtainable  then  a  suffi- 
cient number  of  accumulators  and  of  such  a  size  as  will 
give  the  required  current  must  be  used.  The  writer  has 
always  found  the  Lithanode  very  reliable  and  portable  as 
well  as  giving  a  large  output.  These  can  be  easily  charged 
from  the  main  through  a  lamp  resistance — of  course,  recti- 
fied previously  if  the  current  is  alternating.  If  mains  for 
charging  are  not  available,  then  a  small  gas  engine  or 
motor  dynamo  (direct  shunt  wound)  should  be  used.  Or, 
again,  if  the  latter  is  not  to  be  had  then  they  can  be  charged 
by  a  battery  of  gravity  (CuSo4)  primary  cells,  bearing  in 
mind  that  each  primary  cell  has  a  pressure  of  only  about 
1  volt,  whereas  each  accumulator  cell  has  a  pressure  of 
about  2  volts,  and  also  it  is  necessary  to  have  a  greater 
voltage  in  the  primary  battery  than  in  the  accumulators 
by  about  1|  to  1  volt. 

The  amount  of  current  given  off  from  the  primary  cells 
is  small. 

If  the  x-ray  worker  cannot  have  any  of  the  foregoing 
means  of  obtaining  primary  current,  then  primary  batteries, 
such  as  Grove's  or  bichromate,  are  the  only  resort,  but 
these  give  the  maximum  amount  of  trouble  and  annoyance 
apart  from  greater  expense,  so  much  so  that  the  writer 
would  strongly  advise  them  not  to  be  used. 

Interrupters  or  Breaks. — The  interrupters  for  break- 
ing the  current  in  the  x-ray  coil  may  be  divided  into  (1) 
mechanical  and  (2)  electrolytic. 

The  Hammer  Break  was  the  first  and  acted  in  the  same 
manner  as  the  hammer  of  an  electric  bell.  It  is  now  quite 
obsolete. 


THE  X-RAYS  OR  RONTGEN  RAYS  163 

The  Vril  was  an  improvement  on  the  hammer  break  in 
allowing  more  current  to  pass  into  the  primary  coil,  but  it 
was  somewhat  slow,  and  noisier  than  the  hammer. 

The  Dipper  Break  consists  of  a  wire  worked  by  an 
electro-motor  which  dips  in  and  out  of  mercury,  thus 
making  and  breaking  the  current.  The  mercury  is  con- 
tained in  a  glass  vessel  with  either  methylated  spirits, 
paraffin  or  gas  as  an  electrolyte.  In  working,  the  mercury 
is  apt  to  become  foul  by  reason  of  a  mud  which  forms, 
although  if  an  iron  vessel  is  used  much  less  mud  results, 
consequently  less  cleaning  is  necessary.  To  recover  the 
greater  portion  of  mercury  from  this  mud  it  is  advisable  to 
place  it  in  a  large  dish  to  allow  evaporation  of  the  electro- 
lyte.    No  mud  is  formed  with  coal  gas  as  electrolyte. 

This  break  is  only  suitable  for  low  voltages — say  20  to 
50,  but  it  can  be  used  up  to  100  and  will  pass  a  current  up 
to  20  amperes  or  so.  It  is  somewhat  noisy  to  use.  Either 
large  or  small  currents  are  obtained  by  adjusting  the  vessel 
so  that  the  dipper  will  go  more  or  less  deeply  into  the  mer- 
cury. At  starting  it  is  necessary  to  speed  up  the  motor 
before  switching  on  the  primary  or  short  circuiting  may 
ensue,  and  also  to  switch  off  the  primary  current  before 
stopping  the  motor. 

The  Mackenzie  Davidson  break  is  quieter.  It  consists 
of  a  large  quantity  of  mercury  in  a  box,  into  which  at 
the  surface,  fans  revolve  on  an  axle  from  a  motor  inclined 
at  an  angle  with  the  surface  of  the  mercury.  The  same 
electrolyte  is  used  as  for  the  dipper. 

The .  Jet  Interrupter  is  also  a  mercury  break  in  which 
a  jet  of  mercury  strikes  a  metal  tooth.  Some  are  made 
where  the  mercury  is  pumped  up  by  a  centrifugal  pump, 
the  jet  produced  by  the  revolution  of  the  pump,  causing 
it  to  make  contact  with  the  tooth  and  on  breaking,  sets  up 
a  current.  Others  are  made  where  the  teeth  revolve  and 
the  jets  of  mercury  issue  from  the  side  of  the  containing 
vessel.  The  same  electrolytes  as  for  the  others  may  be 
used.  It  is  worked  by  means  of  an  electro-motor  or  it  can 
be  worked  by  hand.    It  is  a  very  satisfactory  instrument, 


164  ELECTRO-PHYSICS 

the  old  objection  of  clogging  of  the  jet  holes  being  obviated. 
It  can  be  used  for  currents  of  20  amperes  or  more  and  up 
to   240    volts. 

The  Sanax  Interrupter  is  made  on  an  entirely  different 
principle  from  any  of  the  others.  In  this  a  steel  pear-shaped 
vessel  is  attached  to  the  vertical  axle  of  an  electro-motor 
and  contains  a  small  quantity  of  mercury  with  paraffin  as 
the  electrolyte.  Centrifugal  force  causes  the  mercury  to 
rise  up  the  sides  of  the  bowl  until  it  reaches  a  groove.  Thus 
a  ring  of  rotating  mercury  is  formed.  Inside  the  bowl  on  a 
vertical  spindle  placed  eccentrically  is  a  fiber  disk  with  2 
copper  segments  rotated  by  the  mercury  ring  which  makes 
and  breaks  the  current.  This  form  of  break  makes  very 
little  noise  and  has  many  advantages. 

The  Auto-Magnetic  is  very  efficient  and  gives  little  or 
no  trouble.  Briefly  it  consists  of  a  vessel  partly  filled  with 
mercury,  and  coal  gas  as  an  electrolyte.  In  this  vessel  is  a 
horizontal  axle  fitted  with  blades  which  on  revolving  sweep 
in  and  out  of  the  mercury.  No  motor  is  used  but  a  series 
of  field  magnets,  so  that  on  switching  on  the  current  the 
blades  revolve  instantly,  through  the  action  of  the  field 
magnets.  Unlike  some  others  on  the  same  principle  it  can 
be  easily  made  to  travel  either  very  rapidly  or  slowly  and 
also  regulated  to  give  from  \  milliampere  in  the  secondary 
up  to  25  milliamperes. 

The  Electrolytic  Interrupter  consists  of  a  large  glass 
vessel  partly  filled  with  dilute  sulphuric  acid  (sp.  gr.  1200) 
into  which  dips  a  sheet  of  lead  (cathode)  and  also  a  platinum 
wire  (anode)  fitted  into  a  porcelain  holder.  The  platinum 
emerges  from  a  hole  at  the  extremity  of  this  holder  about 
a  quarter  of  an  inch  or  so.  On  switching  on,  the  current 
flows  from  the  platinum  point  to  the  lead  by  reason  of  the 
conductivity  of  the  electrolyte  and  in  doing  so  bubbles  of 
hydrogen  form  on  the  surface  of  the  platinum  thus  breaking 
the  current  but  only  for  an  exceedingly  short  time.  The 
bubbles  breaking  off  again,  the  current  again  flows  when 
the  same  action  takes  place  again.  The  advantage  this 
break  has  over  others  is  its  rapidity  and  the  great  amount  of 


THE  X-RAYS  OR  RONTGEN  RAYS  165 

current  that  can  be  passed.  One,  two,  or  three  anodes  can  be 
fitted  either  to  work  together,  or  as  a  single  or  double  pole. 
The  disadvantage  of  this  break  is  the  liability  to  reverse 
current  which  heats  and  spoils  the  z-ray  tube.  Although  it 
can  work  from  any  voltage  from  50  to  250  yet  probably  100 
volts  is  the  best.  It  also  makes  much  noise  but  this  can  be 
lessened  by  placing  it  in  a  sound-proof  box,  or  attaching  a 
rubber  air  cushion  to  the  porcelain  tube. 

Switchboard.  —  When  two  kinds  of  interrupters  are 
used,  as  a  mercury  and  electrolytic,  a  change-over  switch 
is  necessary  and  this  is  attached  to  the  switchboard  or 
table.  The  necessity  arises  from  the  fact  that  with  a  mer- 
cury break  the  condenser  is  used  in  the  coil,  but  if  an  electro- 
lytic break  is  used,  not  only  must  the  current  be  changed 
over  it  but  also  the  condenser,  not  being  used,  must  be 
"cut  out."  With  this  latter  a  large  current  may  be  put 
through  the  coil,  and  in  the  experience  of  the  writer  the 
best  switch  for  satisfactorily  breaking  the  current  without 
any  fusing  of  the  contacts  is  the  rapid  switch  made  by 
Butt,  which  by  one  movement  of  the  lever  enables  the 
operator  to  make  an  exceedingly  rapid  exposure  or  one  as 
long  as  desired. 

Ammeters  for  measuring  the  current  should  be  used,  but 
voltmeters  are  not  necessary.  To  measure  the  secondary 
currents  milliammeters  are  necessary,  as  without  one  the 
amount  of  current  passing  through  the  tube  is  not  known 
and  the  correct  exposure  a  matter  of  guesswork.  These 
are  usually  fitted  with  shunts,  thus  multiplying  the  reading 
of  the  index,  because  with  a  mercury  break  possibly  only 
2  milliamperes  may  be  passing,  but  when  one  of  the  modern 
mercury  breaks,  taking  a  large  current,  or  the  electrolytic, 
is  used,  as  much  as  20  to  30  milliamperes  or  more  may  be 
passed  through  the  tube;  a  much  higher  reading  is,  there- 
fore, necessary. 

The  Spinctermeter  is  the  name  given  to  the  instrument 
formerly  known  as  the  spark-gap,  and  consists  of  a  pointed 
rod  which  can  be  pushed  near  to  or  drawn  away  from  a  ball 
or  disk  and   measures  the   alternative   spark   gap.     This 


166  ELECTRO-PHYSICS 

shows  arbitrarily  (for  it  varies  according  to  the  apparatus 
and  amount  of  current  passed)  the  resistance  or  penetrative 
power  of  the  tube. 

The  scientific  and  accurate  measurement  is  obtained  by  the 
use  of  a  radiometer,  of  which  there  are  several.  Benoist's 
consists  of  an  aluminium  disk  graduated  in  steps,  having 
in  the  centre  a  thin  silver  plate.  This  is  viewed  through 
the  fluorescing  screen,  and  when  one  of  the  aluminium 
steps  has  about  the  same  transparency  as  the  silver,  the 
hardness  or  penetrative  power  of  the  tube  is  seen  by  the 
number  of  that  step,  so  that  a  tube  can  be  described  as 
being  of  the  hardness  of — say  "No.  8  Benoist." 

X-ray  Tubes.- — These  may  be  divided  into  three  classes; 

1.  Heavy  anode. 

2.  Light  anode. 

3.  Therapeutic. 

The  first  kind  (H.  A.)  is  for  taking  rapid  exposures  and 
some  of  them  are  described  as  being  extra  heavy,  while 
the  L.  A.  is  meant  for  currents  of  2  or  3  milliamperes. 
But  as  a  matter  of  fact  these  L.  A.  tubes  will  sometimes 
withstand  for  a  third  or  a  half  second,  20  milliamperes,  the 
writer  having  had  experience  of  at  least  three  L.  A.  tubes 
which  gave  several  hundred  such  exposures. 

The  third  class  as  their  name  implies  are  solely  for  thera- 
peutic work  giving  off  abundance  of  rays  but  not  having  the 
cathode  and  anticathode  adjusted  for  focus. 

X-ray  tubes  are  made  by  several  makers  both  in  England 
and  on  the  Continent,  each  maker  having  some  special 
method  of  manufacture. 

Miiller  Tubes  are  made  for  long  life  and  if  strained  too 
much,  especially  when  new,  the  vacuum  will  get  low. 
Automatic  regulation  devices  are  attached. 

In  the  Bauer  Tube  the  chief  feature  is  the  valve  for  lower- 
ing the  resistance.  An  infinitesimal  quantity  of  air  being 
admitted  as  desired. 

Some  tube  makers,  as  Cossors,  attach  to  the  tube  an 
automatic  device  for  lowering,  whereby  C02,  instead  of  air, 
is  liberated  into  the  tube.    To  keep  the  anticathode  cool  the 


THE  X-RAYS  OR  RONTGEN  RAYS  167 

rod  holding  it  is  prolonged  to  the  outside  and  fitted  with 
metal  radiators  so  as  to  cool  it  by  contact  with  the  air. 

Another  method  is  to  have  water  in  contact  with  the 
back  of  the  anticathode,  and  another:  .copper  tongs  are 
inserted  close  to  the  anticathode  and  can  be  withdrawn 
and  plunged  into  water  to  cool. 

The  oscilloscope  tube  is  employed  to  detect  any  trace 
of  reverse  current,  and  consists  of  a  cylindrical  exhausted 
glass  tube  about  8  inches  long  by  1J  inches  in  diameter, 
containing  2  aluminium  wires  of  equal  length  nearly  touch- 
ing, with  a  disk  of  mica  in  the  middle  of  the  tube  having  a 
central  hole.  If  the  current  is  unidirectional  a  blue  fluo- 
rescence is  seen  about  the  wire  in  one-half  of  the  tube,  but 
if  any  reverse  is  present  the  fluorescence  is  seen  more  or 
less  on  both  wires,  showing  the  amount  of  reverse  current. 


TECHNIQUE  OF  DENTAL  RADIOGRAPHY.1 

The  variety  of  uses  to  which  the  Rontgen  ray  has  been 
put  in  the  profession  of  dentistry  has  assumed  such  di- 
mensions, that  but  little  justice  can  be  done  to  this  im- 
portant subject  in  the  comparatively  small  space  that  can 
be  devoted  to  it  in  this  work.  For  a  more  exhaustive 
study  of  this  valuable  addition  to  dental  science  the  reader 
is  referred  to  those  works  which  treat  on  that  subject 
exclusively,  the  most  scientific  of  which,  as  far  as  the  writer 
is  informed,  is  the  Atlas,  etc.,  of  Prof.  Dieck,2  of  the  Berlin 
University  (which  will  soon,  it  is  hoped,  be  published  in 
the  English  language),  and  the  pamphlet  by  Port  and 
Peckert.3  Other  writers  who  have  contributed  valuable 
literature  on  this  subject  are  H.  R.  Raper,  Rollins,  Williams, 
Pfahler,  Tousey,  Cieszynski,  Price,  Cryer,  Sydney  Lange 

1  By  Dr.  C.  H.  Abbot,  of  Berlin. 

2  "Archiv  und  Atlas  der  normalen  und  pathologischen  Anatoniie  in 
typischen  Rontgen  Bildern.  Anatoniie  und  Pathologie  der  Ziikne  und 
Kiefer  irn  Rontgenbilde."    Dieck. 

3  Ueber  die  Rontgenphotographie  in  der  Zahnheilkunde,"  Von  Prof. 
Dr.  Port  und  Privatdozent  Dr.  Peckert-Heidelberg. 


168  ELECTRO-PHYSICS 

of  Cincinnati,  van  Woert,  Rhein,  Shenton,  etc.  The  writer 
hopes,  however,  by  the  following  sketch  of  the  various 
applications  of  this  branch  of  electricity  in  dentistry  to 
incite  the  reader  to  adopt  its  use  in  the  practice  of  his 
profession.  The  properties  and  production  of  the  rays  are 
described  elsewhere  in  this  work. 

The  following  description  of  the  appliances  connected 
with  the  technique  of  dental  radiography  will  provide 
some  useful  hints  to  the  operator  for  obtaining  the  best 
results. 

One  of  the  most  important  considerations  is  the  de- 
termination of  the  resistance  or  vacuum  of  the  tube,  and 
for  this  purpose  a  number  of  appliances  have  been  devised, 
such  as  the  Walter  and  Benoist  scales,  Wehnelt's  crypto- 
radiometer,  Beez's  scale,  and,  last  but  not  least,  Bauer's 
"Qualimeter,"  by  means  of  which  the  resistance  of  different 
tubes  can  be  gauged — given  the  same  amperage  and  voltage 
of  the  current  prior  to  its  entering  the  tube. 

The  human  hand  was  at  first  most  frequently  used  for  the 
determination  of  the  so-called  degree  of  "hardness"  of  the 
tube,  as  it  was  very  convenient  and  afforded  a  most  re- 
liable means  for  this  purpose  to  the  experienced  operator; 
but  the  disastrous  results  of  this  method,  which  was  long 
in  use  before  the  danger  was  realized,  are  now  too  well  known 
to  require  further  comment.  "Skeleton"  hands  have  been 
used  in  dark  boxes  with  a  fluorescent  screen,  similar  to  the 
Wehnelt  scale,  and  Dieck  has  devised  a  cryptoscope  con- 
taining a  section  of  the  lower  jaw  with  teeth,  incased  in 
wax  so  as  to  imitate  approximately  the  density  of  the  sur- 
rounding soft  tissues.  These  have  proved  very  efficient  in 
general  use. 

The  resistance  most  adapted  to  general  dental  work  is 
about  6  to  6|  on  the  Wehnelt  cryptoradiometer  (6  to  6| 
Wehnelt  for  short).  One  of  the  advantages  of  the  Wehnelt 
is  that  there  is  no  need  for  darkening  the  room,  as  the 
padded  box  can  be  pressed  close  to  the  eyes  so  that  no 
disturbing  light  is  noticeable.  It  has  one  disadvantage, 
however,  in  that  the  subjective  or  personal  element  gives 


THE  X-RAYS  OR  RONTGEN  RAYS  169 

rise  to  discrepancies,  as  human  eyes  do  not  all  see  quite 
alike,  and  differences  of  impression  of  as  much  as  1  to  2 
units  have  been  registered  by  different  persons  using  the 
same  scale  on  the  same  tube.  The  proper  resistance  of 
the  tube  depends  upon  the  thickness  and  density  of  the 
object  to  be  a'-rayed;  for  example,  a  radiograph  of  the  whole 
skull  would  require  a  tube  with  the  resistance  of  about 
9  to  10  Wehnelt. 

The  writer  has  found  the  Bauer  qualimeter  used  under 
the  above-mentioned  conditions  a  most  reliable  and  satis- 
factory stand-by,  for  it  does  away  with  the  more  or  less 
difficult  comparison  of  shades,  and  registers  the  condition 
of  the  tube  in  plain  numbers.  This,  as  well  as  all  other 
methods,  however,  has  a  slight  drawback,  inasmuch  as  it 
takes  some  few  seconds  for  the  indicator  to  cease  oscillating 
and  to  point  to  the  number  in  question,  thus  permitting 
the  tube  to  grow  a  trifle  "  harder"  by  virtue  of  its  longer 
use,  but  with  a  little  experience,  the  observer  will  be  able 
to  anticipate  the  eventual  point  of  rest. 

The  following  table  compares  the  principal  scales: 

Bauer     ...  1.0  2.0  3.0  4.0  5.0  6.0  7.0  8.0  9.0  10 

Wehnelt       .      .  1.5  3.0  4.5  6.0  7.5  9.0  10.5  12.0  13.5  15 

Walter   .      .      .  1.0  1-2  2-3  3-4  4-5  5-6  6-7  7-8 

Benoist         .      .  1.0  2.0  3.0  4.0  5.0  6.0  7.0  8.0  9.0  10 

To  determine  the  proper  direction  of  the  rays,  the  stand 
is  of  great  importance.  In  the  writer's  opinion,  the  Lam- 
bertz  stand  modified  by  Dieck,  is  the  most  efficient. 

The  horizontal  tube-holder  can  be  easily  raised  or  low- 
ered on  the  perpendicular  shaft,  and  by  means  of  a  second 
horizontal  shaft  regulated  by  a  cog-wheel  it  can  be  length- 
ened and  shortened.  A  ball-and-socket  joint  at  the  end  of 
the  horizontal  arm  permits  the  turning  of  the  tube-box  in 
every  direction,  and  of  its  easy  adjustment.  Lately  the 
whole  end-joint  of  the  arm  has  been  made  to  turn  around 
the  perpendicular  axis,  which  facilitates  still  further  the 
fixing  of  the  tube  at  the  required  angle.  The  centralizing 
telescope  which  is  attached  to  a  hinge  and  pushed  aside 


170 


ELECTRO-PR  YSICS 


before  the  current  is  turned  on,  is  a  valuable  device,  which 
permits  of  the  most  accurate  adjustment;  it  can  also  be  used 
as  a  visor  for  determining  the  centre  of  the  target.  To 
insure  absolute  correctness  of  focus  the  current  should  be 


Fig.  75 


The  Lambertz  stand. 


THE  X-RAYS  OR  RONTGEN  RAYS 


171 


turned  on  and  the  rays  allowed  to  pass  through  the  tube,  a 
small  and  perfect  luminous  disk  should  appear  on  the  fluor- 
escent screen.  The  cylinder  of  x-ray-proof  material,  provided 
with  an  adjustable  diagram,  cuts  out  the  secondary  rays 
which  do  so  much  to  impair  the  sharpness  of  the  radio- 
graph, and  of  which  more  will  'be  said  later. 

When  the  operator  is  in  a  position  to  direct  the  rays  in  a 
straight  line  through  the  middle  of  the  cylinder,  the  next 
question  he  must  consider  is  the  relation  of  this  line;  firstly, 
to  the  axis  of  the  tooth  or  root,  and,  secondly,  to  the  plane 
of  the  film  or  plate;  and  here  he  must  observe  certain  prin- 
ciples of  projection  which  in  themselves  are  simple,  but 
which  it  may  be  well  to  recall. 


Fig.  77 


The  first  is  the  consideration  of  the  relative  distances 
between  the  target,  the  object  to  be  a'-rayed  and  the  film 
or  plate,  and  the  effect  of  these  upon  the  size  of  the  skia- 
graph compared  to-  the  object  itself.  This  may  be  easily 
illustrated  by  the  accompanying  diagrams,  and  roughly 
stated  by  the  following  self-evident  rule. 

T  being  the  target,  cd  and  C\di  the  object  to  be  .T-rayed, 
and  p  the  film  or  plate,  the  nearer  the  object  cd  is  to  the 


172 


BLECTRO-PH  YSICS 


plate,  the  smaller  the  image  ah  will  be,  and  the  further 
from  the  plate,  the  larger  the  image  Cidi  will  be  on  plate 
ciidi;  the  distance  from  T  to  the  plate  remaining  the  same; 
and  as  shown  in  Fig.  77  the  distance  between  the  object 
cd  and  plate  p,  remaining  the  same,  the  image  of  the  object 
will  be  larger,  the  nearer  the  target  is  to  the  plate,  ah 
produced  by  the  rays  starting  at  T  is  longer  than  ai&i  with 
the  target  at  7\. 

The  distance  between  the  target  and  the  plate  or  film 
in  dental  radiographs  should  usually  be  about  35  cm.  with 
the  film  pressed  as  closely  to  the  alveolus  as  possible.  In 
taking  radiographs  of  the  teeth  of  the  upper  jaw;  with  the 
plate  or  film  held  between  the  teeth  and  taken  from  above, 
the  distance  should  not  be  less  than  35  to  40  cm. 


Fig.  78 


Imag inary  Dividing 


Line 


The  direction  of  the  rays  in  their  relation  to  the  axis  of 
the  roots  (especially  in  the  upper  teeth)  and  the  plane  of 
the  film  is  of  great  importance  in  producing  an  approxi- 
mately correct  image  of  the  tooth  or  root  on  the  film,  and 
here  the  rules  advocated  by  Cieszynski  and  Dieck  should 
be  observed  as  closely  as  possible,  provided  there  are  no 
other  conditions,  such  as  can  only  be  brought  out  by  a 
distorted  picture;  this,  however,  will  be  referred  to  later. 


THE  X-RAYS  OR  RONTGEN  RAYS 


173 


The  rule  to  be  observed  is  to  direct  the  rays  vertically 
through  the  apex  of  the  root  in  question  on  to  an  imaginary 
line  dividing  the  angle  formed  by  the  axis  of  the  root  and 
the  plane  of  the  film.     This  is  shown  in  Fig.  78. 

An  instrument  devised  by  Dieck  for  this  purpose  is 
shown  in  Fig.  79 

Fig.  79 


The  more  the  rays  are  directed  from  above,  the  more 
fore-shortening  of  the  tooth  will  occur,  and  the  more  from 
below  the  more  elongated  the  teeth  will  appear  on  the  film. 

Occasionally  it  may  be  important  to  procure  an  exact 
measurement  of  the  length  of  a  root,  which  can  easily  be 
ascertained  provided  the  operator  can  insert  a  broach  of 
a  given  length  into  a  part  of  the  canal  before  exposure. 
This  can  be  calculated  by  the  following  proportion: 

If  the  length  of  our  broach  ab  is  known  on  the  radio- 
graph we  can  measure  the  length  of  the  image  of  the  root 


174 


ELECTRO-PHYSICS 


a'c',  also  of  the  broach  a'b'.    The  actual  length  of  the  root 
to  be  calculated  being  x  we  have  the  proportion : 


a  b' :  ab  =  a'c' :  x 


or,  for  example,  if 


ab  X  a'c' 

x  =  

a'b' 

ab   =  6  mm. 
a'b'  =  8  mm. 
a'c'   =  10  mm., 
we  have       8:6  =  10  :  x 

6  X  10 


and 


=  7.5  mm. 


Fig. 


h 


In  taking  .r-rays  of  teeth  in  the  lower  jaw  the  placing  of 
the  film  is  comparatively  simple  for  the  incisors,  bicuspids, 
and  molars;  for  the  canines,  owing  to  their  occupying  a  more 
or  less  "corner"  position  in  the  arch,  the  holding  of  the  film 
is  not  always  a  simple  matter,  for  unless  it  is  very  narrow 
it  will  bend  a  great  deal,  causing  considerable  distortion, 
especially  of  the  adjoining  teeth.  In  cases  where  it  is 
desirable  to  include  the  apex  of  the  roots  and  the  parts 
underlying  them,  especially  in  lower  wisdom  teeth,  the 
operator  often  encounters  a  good  deal  of  opposition  on  the 
part  of  the  patient,  on  account  of  the  irritation  to  the  soft 
tissues  caused  by  the  wrapping  of  the  film.  A  film-holder 
which  obviates  this  difficulty  is  described  in  another  part 
of  this  chapter. 

In  cases  where  the  formation  of  the  lower  jaw  is  such 
that  it  is  difficult  or  impossible  to  obtain  a  view  of  the 
apex,  or  parts  underlying  it  (as  for  example  an  abscess- 
cavity  or  cyst)  without  distortion,  it  will  be  well  to  direct 
the  rays  considerably  from  below  in  order  to  include  these 


THE-  X-RAYS  OR  RON T GEN  RAYS 


175 


portions,  although  this  will  produce  a  somewhat  distorted 
image.  But  where  it  is  a  matter  of  locating  an  abscess- 
cavity  or  cyst,  this  is  of  no  consequence  compared  to  the 
establishment  of  the  point  in  question. 


Fig.  81 


_^r 


The  interpretation  of  the  film  or  plate  is  naturally  fully 
as  important  as  its  production,  and  ,it  should  be  kept  in 
mind  that  what  is  seen  is  the  effect  of  the  difference  of 
absorption  which  the  rays  undergo  in  their  passage  through 
the  tissues  which  they  penetrate.  This  again  depends  on 
the  density  and  thickness  of  the  object,  or  the  combined 
densities  and  thicknesses  of  superimposed  layers  of  differ- 
ent structures  such  as  roots,  bone,  pus,  filling  materials,  etc. 
For  instance,  the  overlapping  part  of  a  buccal  molar  root 
over  part  of  a  palatal  one,  might  give  to  the  unobserving 
a  misleading  picture,  when  proper  reasoning  will  put  the 
operator  right.  The  designation  "positive"  and  "negative" 
in  works  on  the  Rontgen  ray  is  often  a  little  confusing. 
In  most  text-books  the  illustrations  consist  of  prints  of 
the  films,  while  in  practice  the  operator  generally  uses  the 
original  film  itself.  On  the  latter  the  teeth  and  bones  show 
light,  and  the  softer  tissues  and  cavities  appear  dark,  as 
they  offer  the  least  resistance  to  the  passage  of  the  rays;  on 
the  former,  of  course,  the  reverse  is  the  case,  and  as  the 
prints  or  positives  are  generally  used  as  illustrations  in  the 
text-books,  the  respective  shadows  will  be  referred  to  as 


176  ELECTRO-PHYSICS 

they  appear  in  these  positives,  unless  otherwise  expressly 
designated. 

In  the  interpretation  of  radiographs  there  are  a  few 
anatomical  points  to  be  recalled,  the  neglect  of  which  might 
at  times  lead  to  a  misleading  diagnosis.  One  source  of 
error  may  be  a  small  spot  on  the  film  caused  by  the  anterior 
palatine  foramen,  which  may  be  mistaken  for  destruction 
of  bone  resulting  from  abscess. 

The  mental  foramen  also  may  give  rise  to  the  same 
faulty  diagnosis,  although  more  rarely,  owing  to  its  lower 
position  in  the  inferior  maxilla. 

Fig.  82 


Film 


The  suspicion  that  molar  or  bicuspid  roots  may  be  pro- 
jecting into  the  antrum  is  also  often  suggested  to  the  oper- 
ator by  the  appearance  of  the  film,  and  a  correct  diagnosis 
may  be  very  difficult  without  accurate  observation  and 
reasoning.  If  the  topography  of  the  antrum  is  considered 
in  its  relation  to  the  roots  of  the  molars  and  bicuspids  and 
the  hard  palate,  it  will  be  easily  understood  that  owing  to 
the  slanting  direction  of  the  rays  from  above  downward, 
one  or  more  roots  of  the  above-named  teeth  are  often  pro- 
jected into  the  image  of  the  antrum.    Of  the  molars  this  is 


THE  X-RAYS  OR  RONTGEN  RAYS  177 

most  f requently  the  case  with  the  palatal  root  (Fig.  82) .  The 
question  of  perforation  of  the  floor  of  the  antrum  by  a  dis- 
eased root  requires  a  very  sharp  radiograph,  marking  the 
contrasts  very  clearly  and  showing  whether  the  pericemen- 
tum and  periosteum  of  the  alveolus  are  intact  or  not.  The 
walls  of  the  alveolus  will  show  as  a  light  line  on  the  film, 
and  the  space  occupied  by  the  pericementum  as  a  dark 
line.  In  any  case  presenting  the  least  doubt,  two  or  more 
exposures  should  be  made  from  different  directions. 

The  question  as  to  which  one  of  two  (or  more)  teeth  or 
roots  partly  lying  in  the  line  of  the  rays  is  before  or  behind 
the  other,  is  one  which  may  also  arise  in  practice.  This 
may  not  be  an  easy  matter  to  decide  without  the  aid  of 
stereoscopic  radiographs,  but  the  tooth  which  appears  rela- 
tively the  smallest  and  most  sharply  outlined  will  obviously 
be  the  one  nearest  the  film  and  consequently  nearest  the 
palate  in  the  superior  maxilla,  or  if  they  are  lower  teeth, 
nearest  the  lingual  wall  of  the  mandible. 

The  proper  time  of  exposure  is  of  the  utmost  impor- 
tance in  obtaining  satisfactory  results  in  x-ray  work.  Here 
again  it  is  very  difficult  to  advise  the  beginner  as  so  much 
depends  upon  the  strength  of  the  primary  current,  the  size 
of  the  induction  coil  or  whatever  apparatus  the  operator  is 
using. 

With  a  coil  furnishing  a  spark  40  to  50  cm.  and  a  primary 
current  of  25  to  35  amperes  and  a  tube  of  approximately 

5  to  6  Wehnelt  (units)  the  operator  should  under  ordinary 
conditions  obtain  excellent  results  with  an  exposure  of  from 

6  to  8  seconds,  unless  the  bone  is  exceptionally  dense,  when 
a  somewhat  longer  exposure  should  be  made.  The  time 
for  taking  the  lower  molars  (especially  second  and  third) 
should  be  about  double  that  for  the  front  teeth,  owing  to 
the  greater  thickness  of  bone  to  be  penetrated.  Practice 
will  be  the  best  teacher  in  this  respect.  Less  powerful 
outfits  will  necessitate  relatively  longer  exposures. 

The  most  desirable  apparatus  for  those  to  whom  expense 
is  no  consideration  is  the  "Ideal  Outfit"  manufactured  by 
Reiniger,  Gebbert  &  Schall,  based  on  the  original  idea  of 
12 


178  ELECTRO-PHYSICS 

Snook,  which  contains  a  very  ingenious  device  for  changing 
the  high  tension  alternating  current  into  a  continuous  one, 
also  of  high  tension,  which  is  ideal  for  obtaining  the  most 
perfect  Rontgen  rays.  In  this  outfit  the  exposures  can 
be  cut  down  to  a  fraction  of  a  second,  but  an  exposure  of 
about  two  seconds  with  a  less  powerful  current  furnishes 
the  best  results.  For  nervous  patients  or  children,  or  in 
cases  where  the  insertion  of  the  film  at  the  back  of  the 
mouth  is  liable  to  cause  choking  or  nausea,  the  possibility 
of  cutting  down  the  exposures  to  that  extent  is  a  distinct 
advantage  which  can  be  readily  understood. 

The  operator  working  with  a  more  modest  outfit  has 
also  a  means  of  abbreviating  his  exposures,  viz.,  by  using 
the  so-called  intensifying  screens  with  his  films.  This 
screen  consists  of  card-board  covered  on  one  side  with  a 
preparation  principally  containing  Tungsten  or  Wolfram 
which  fluoresces  and  absorbs  the  x-rays  to  a  marked  degree, 
acting  on  the  film  or  plate  for  some  time  after  the  exposure; 
it  is  therefore  undesirable  to  leave  the  plate  packed  with 
the  screen  long,  for  fear  of  causing  overexposure.  One 
drawback  with  these  intensifiers  is  that  they  are  liable  to 
fog  the  radiograph  to  some  extent  and  that  they  do  not 
keep  very  long  without  losing  some  of  their  strength.  Still, 
when  we  consider  that  they  are  capable  of  reducing  the 
time  of  exposure  at  least  ten-fold,  we  cannot  but  acknowl- 
edge that  they  certainly  should  have  their  place  in  every 
outfit  except  the  above-mentioned  "Ideal."  The  screen 
is  best  applied  by  packing  it  with  its  glossy  side  facing  the 
sensitized  side  of  the  film. 

Another  of  the  numerous  devices  of  Prof.  Dieck  for  per- 
fecting dental  radiographs  is  a  very  simple  instrument 
shown  in  Fig.  83.  We  know  that  the  Rontgen  rays  will 
penetrate  thin  or  less  dense  portions  of  bone  more  readily 
than  thick  or  hard  layers;  if,  therefore,  the  territory  to  be 
x-rayed  includes  both  varieties  (such  as  will  be  the  case  in 
an  exposure  of  the  whole  superior  maxilla  with  the  teeth, 
taken  from  above)  the  incisors  and  perhaps  the  canines 
will    appear   very   distinctly,    whereas   the    bicuspids    and 


THE  X-RAYS  OR  RON T GEN  RAYS 


179 


molars,  presenting  larger  dimensions,  will  be  under- 
exposed. To  obviate  this  fault  and  enable  the  operator 
to  obtain  a  more  uniform  exposure,  a  little  plate  of  lead, 


Fig.  83 


Lead  plates  used  to  retard  action  of  rays. 


180  ELECTRO-PHYSICS 

attached  to  a  wooden  handle,  is  passed  to  and  fro  before  the 
thinner  part,  to  retard  the  action  of  the  rays  while  allowing 
them  to  penetrate  the  denser  portions.  Thus  with  a  little 
practice  the  operator  can  obtain  a  uniform  appearance  of 
structures  of  different  densities  on  the  same  plate. 

Stereoscopy  in  Dental  X-ray  Work. — It  is  easily  understood 
that  x-ray  stereoscopy  differs  from  ordinary  stereoscopy, 
inasmuch  as  the  exposures  are  made  consecutively  with 
the  same  tube,  which  is  moved  a  certain  distance  from 
either  side  of  the  position  from  which  the  simple  x-ray 
would  be  taken.  The  plane,  of  course,  must  be  the  same 
and  the  film  or  plate  must  be  placed  in  the  same  position 
for  the  second  that  it  occupies  during  the  first  exposure. 
A  stereoscopic  tube  with  two  cathodes  and  anticathodes, 
the  focal  centres  of  which  are  placed  5  to  6  cm.  apart,  has 
been  devised  by  Fiirstenau,  but  this  seems  hardly  necessary 
with  the  graduated  scale  on  the  Lambertz  stand. 

In  this  connection  it  will  be  well  to  bear  in  mind  that 
stereoscopy  is  not  to  be  depended  upon  for  furnishing 
absolutely  correct  relations  of  the  different  parts.  This 
conclusion  is  amplified  by  the  fact  that  there  is  so  much 
diversity  of  opinion  among  different  authorities  as  to  the 
proper  distance  to  which  the  tube'  should  be  moved  away 
from  the  median  line  for  the  two  exposures.  The  distance 
should  approximate  that  of  the  eyes  from  each  other. 
Some  say  that  this  should  be  6,  others  advise  7  cm.  Marie 
and  Ribaut  have  published  a  table  giving  a  number  of 
different  figures1  varying  from  2  cm,  to  10  or  even  16  cm. 
for  the  displacement  of  the  tube  in  axray  stereography 
according  to  the  distance  of  the  part  in  question  from  the 
anticathode,  and  the  thickness  of  the  object.  This  does 
not  appear  very  rational,  as  the  distance  separating  the 
human  eyes  does  not  vary  to  such  an  extent.  Albers- 
Schonberg,2  as  well  as  Kells,3  in  their  work  describe  a  com- 
plicated apparatus,  giving  to  the  tube   not  only  a  lateral 

1  Archives  d'Electricite  medicale,  15  juillet,  1899. 

2  "Die  Rontgentechnik,"  von  H.  Albers-Schonborg, 

3  Dental  Cosmos,  July,  1912. 


THE  X-RAYS  OR  RONTGEN  RAYS  181 

but  a  rotary  displacement  for  the  most  powerful  rays  to 
pass  through  the  object  to  be  stereographed.  But  this 
seems  to  the  writer  unnecessary,  as  the  rays  spread  fan-like 
from  the  target,  and  those  striking  the  object,  although 
not  the  most  central  ones,  still  are  strong  enough  to  pro- 
duce excellent  results.  The  distance  from  target  to  film 
or  plate  should  not  be  less  than  35  cm.;  for  the  whole  head 
it  should  be  at  least  50  cm.  Stereoscopic  radiographs  are 
not  reliable  for  giving  very  exact  values,  but  nevertheless 
in  a  certain  number  of  cases  a  good  stereographic  radio- 
graph will  be  a  considerable  aid  in  diagnosis.  Such  cases 
include  large  abscess-cavities  in  which  it  is  of  importance 
to  get  an  idea  not  only  of  their  breadth,  but  of  their 
depth;  irregularities  where  the  relative  position  of  the  teeth 
cannot  be  sufficiently  established;  severe  cases  of  pyorrhoea, 
necrosis,  etc. 

A  few  years  ago  there  was  considerable  discussion  about 
the  feasibility  of  examining  the  teeth  with  a  fluorescent 
screen,  or  taking  radiographs  with  the  anticathode  of  a 
tube  of  suitable  dimensions  and  construction  inside  the 
mouth.  Tousey  tried  these  tubes,  also  Guye  of  Geneva  and 
Bauer  of  Berlin,  but  these  methods  were  soon  abandoned 
on  account  of  the  very  considerable  danger  to  the  patient. 
The  idea  of  simply  placing  a  little  tube  in  the  patient's 
mouth,  holding  the  plate  wherever  desired  and  turning 
on  the  current,  is  very  alluring,  but  other  considerations 
make  it  appear  less  so,  especially  the  prospect  of  the 
patient  sustaining  severe  burns  for  which  the  operator  is 
responsible. 

Extra-oral  exposures  in  which  the  film  or  plate,  as  well 
as  the  tube  is  held  outside  of  the  mouth,  often  become 
necessary  when  larger  portions  of  the  maxilla  or  other 
bones  of  the  head  are  involved. 

Here  the  operator  will  do  well  to  refresh  his  memory  in 
regard  to  the  topographical  anatomy  of  the  head  and  neck, 
as  the  overshadowing  of  the  parts  to  be  examined  by 
various  other  portions  of  bone  may  give  rise  to  many  errors 
in  diagnosis. 


182 


ELECTRO-PHYSICS 


It  is  rarely  possible  to  obtain  a  large  radiograph  of  this 
kind  without  distortion  of  some  part  or  other,  but  that 
does  not  necessarily  make  it  any  less  valuable,  as  in  most 
cases  the  necessary  allowances  can  be  made  to  arrive  at 
correct  conclusions;  but  where  it  is  possible  to  avoid  such 
a  condition  it  is  preferable  to  do  so.  For  this  purpose  a 
"phantom"  skull  attached  to  a  stand  has  been  devised  by 
Dieck,  which  is  placed  so  that  the  centralizing  telescope 
of  the  protective  box  containing  the  tube  may  be  adapted 
to  it  in  a  position  similar  to  the  one  to  be  occupied  by  the 
patient's  head  during  the  exposure. 

Regarding  the  packing  or  wrapping  of  the  films  used 
in  dental  a>ray  work,  Price  has  advocated  placing  a  piece 
of  black  or  red  rubber  base-plate  on  both  sides  of  the 
film,  with  the  edges  extending  a  millimeter  or  two  beyond 
the  film  and  pressing  them  tightly  together  to  exclude  all 
light.  Black  and  red  should  be  used  together  so  as  to 
mark  the  sensitized  side  of  the  film,  which  should  be  placed 
toward  the  tube;  two  films  are  often  placed  together  to 
get  two  radiographs  at  the  same  exposure.  If  it  be  im- 
portant to  include  deep-lying  portions  of  the  lower  jaw, 
one  piece  of  rubber  plate  only  should  be  employed  of 
double  the  size,  folded  over,  and  the  edge  thus  diminished 
to  the  thickness  of  the  base-plate  where  most  necessary 
(Fig.  84). 

Fig.  84 


The  wrapping  most  universally  employed,  however,  up 
to  the  present  date  is  black  paper,  and  in  most  cases  it 
accomplishes   the   object   perfectly.      At   least   two   layers 


THE  X-RAYS  OR  RONTGEN  RAYS  183 

should  be  used,  either  both  black,  or  one  black,  and  outside 
of  that  a  good  red  oil-paper,  which  is  smooth  and  excludes 
the  light  perfectly.  The  corners  of  these  paper  wrappings 
are  sometimes  objectionable  for  they  irritate  the  soft  tissues, 
especially  in  the  lower  jaw.  A  number  of  ingenious  devices 
have  been  thought  out  for  holding  the  film  in  place  in  the 
mouth.  Among  others,  a  hardened  Stents  impression, 
trimmed  to  suit  the  needs  of  the  case,  has  been  recommended. 
Cieszynski  has  constructed  film-holders  for  the  upper  and 
lower  jaw,  the  upper  one  consisting  of  a  metal  frame  to 
be  held  in  position  by  the  bite  of  the  patient,  aided  by  the 
use  of  a  rubber  bag  to  be  inflated  after  the  film  has  been 
inserted.  The  writer,  however,  considers  that  up  to  the 
present  nothing  surpasses  the  human  finger  as  a  plate- 
holder  for  general  use,  and  were  it  not  for  a  certain  danger 
to  the  operator  or  the  assistant  who  lends  his  hand  to  this 
purpose,  this  simple  method  would  be  the  best. 

Danger  of  X-ray  to  Patient  and  Operator. — As  regards 
the  patient,  the  danger  of  x-rays  can  be  very  readily  dis- 
missed from  the  mind  so  far  as  radiographs  are  concerned, 
for  the  exposures,  even  the  longer  ones,  are  now  too  short 
to  do  even  a  child  the  least  harm,  unless  the  operator  is 
guilty  of  the  grossest  negligence.  The  consideration,  how- 
ever, is  immeasurably  more  serious  in  the  case  of  those 
who  occupy  themselves  with  this  work  extensively.  It  has 
been  stated  before  that  the  hand  should  never  be  employed 
as  a  means  of  testing  the  tube,  and  the  bare  fingers  should 
be  used  only  in  the  rarest  and  most  urgent  cases,  where  a 
protective  glove  is  too  bulky.  This  glove  should  form 
part  of  every  dental  x-ray  outfit,  and  can  be  purchased 
at  the  regular  x-ray  supply  stores.  These  gloves  are  made 
of  a  protective  material  consisting  of  thick  rubber  cloth 
impregnated  with  metal,  and  are  well-nigh  absolutely 
impervious  to  the  rays.  A  compromise  between  a  glove 
and  a  mitten  has  been  used  in  the  writer's  surgery  for  some 
years  and  has  given  much  satisfaction.  It  consists  of  a 
thumb  and  forefinger,  and  a  casing  for  the  other  three 
fingers  together;  it  is  somewhat  clumsy,  but  serves  to  hold 


184  ELECTRO-PHYSICS 

the  film  well  in  place  when  once  the  same  has  been  properly ' 
inserted  without  the  glove,  which  can  be  slipped  on  while 
the  film  is  temporarily  held  with  the  other  hand.  Tousey 
mentions  another  way  to  make  protective  gloves:  soak 
thick  leather  gloves  in  a  saturated  solution  of  bismuth 
chloride,  then  immerse  in  cold  running  water  for  an  hour. 
Repeat  three  or  four  times.  This  method  is  published  by 
Dr.  Win.  Mitchell,  Archives  of  the  Rontgen  Ray,  April,  1908. 

The  question  of  secondary  rays  is  one  of  such  importance 
that  it  must  be  touched  upon  here,  for  not  only  do  these 
rays  expose  the  operator  to  a  certain  amount  of  danger  but 
they  impair  the  clearness  of  the  radiograph. 

The  impact  of  the  primary  Rontgen  rays  upon  any 
solid  or  liquid  body  gives  rise  to  rays  which  are  called 
secondary;  they  radiate  in  all  directions  from  the  point 
of  impact  and  act  similarly  to  reflected  rays;  consequently 
they  may  to  some  extent  be  dangerous  to  those  exposed 
to  them,  although  they  are  not  as  powerful  as  the  primary 
rays  and  possess  certain  properties  that  differ  from  them. 

The  other  great  disadvantage  of  these  secondary  rays 
is  their  effect  upon  the  sharpness  of  the  image  on  the  plate. 
They  arise  from  contact  with  the  wall  of  the  tube  and  are 
more  or  less  readily  cut  out  by  the  lead  cylinder  attached 
to  the  Lambertz  stand,  but  this  does  not  do  away  with  the 
secondary  rays  originating  in  the  body  itself  which  is  to 
be  rc-rayed,  for  these  are  beyond  the  pale  of  the  cylinder, 
and  their  effect  could  only  be  eliminated  by  interposing 
another  cylinder  of  suitable  dimensions  between  the  object 
and  the  sensitive  plate.  But  such  an  one,  with  a  diameter 
large  enough  to  include  all  of  the  desired  image,  would 
have  to  be  too  long  to  be  practicable;  in  other  words,  it 
would  remove  the  body  too  far  from  the  plate.  Dr.  G. 
Bucky,  of  Berlin,  does  away  with  this  necessity  in  a  most 
ingenious  way.  He  reasoned  that  the  smaller  the  diameter 
of  the  cylinder  the  nearer  the  object  could  be  approached  to 
the  plate,  so  he  constructed  a  series  of  small  compartments 
of  only  one  or  two  centimeters  in  length  with  correspond- 
ingly  small  diameters,   and  walls   converging  toward   the 


THE  X-RAYS  OR  RONTGBN  RAYS  185 

focal  centre  of  the  tube.  The  results  are  most  remarkable. 
The  image  on  the  plate  by  this  method  is  divided  by  a 
grille  or  net-work  of  many  fine  lines,  but  this  can  hardly 
be  called  a  drawback  compared  to  the  increased  clearness 
of  the  image,  and  in  many  cases  it  may  even  be  deemed 
an  advantage,  as  it  furnishes  a  scale  of  measurement  that 

Fig.  85  Fig.  86 


Dotted  lines  indicate  secondary  rays. 

may  be  very  desirable.  The  grille  is  being  manufactured 
by  Siemens  &  Halske,  of  Berlin,  and  will  soon  be  on  the 
market.  Its  use  for  dental  work  is  restricted  to  those  cases 
where  a  plate  of  some  size  is  desired,  such  as  for  diagnosis 
of  troubles  of  the  antrum  or  frontal  sinus;  in  these  cases  it 
should  prove  invaluable. 

X-RAY  DIAGNOSIS.1 

Under  various  headings  some  of  the  uses  to  which  the 
x-ray  is  put  in  dentistry  are  as  follows: 

A.  For  purposes  of  diagnosis. 

B.  For  therapeutic  purposes. 

1  By  Dr.  C.  H.  Abbot,*  of  Berlin. 


186  ELECTRO-PHYSICS 


I.     In  the  detection  and  location  of  unerupted  or 
impacted  teeth  in  the  practice  of  orthodontia. 
In  the  determination  of: 

II.  The  length,  shape,  and  direction  of  roots;  (a)  for 
crown  and  bridge  work,  (b)  for  extraction  (espe- 
cially of  the  lower  wisdom  teeth) . 

III.  The  amount  of  absorption  of  roots  or  bone. 

IV.  The  destruction  of   bone  as  a  result  of   alveolar 

abscess. 
V.    The  presence  of  cysts. 
VI.    The  destruction  of  the  alveolus  in  pyorrhoea. 
VII.     The  position  of  broken-off  nerve  broaches  or  other 

instruments. 
VIII.     Fractures  of  roots. 
IX.     The  existence  of  pulp  stones  or  deposits  of  bone 

in  pulp  chamber. 
X.     Caries  of  roots  under  crowns  or  caps,  and  approxi- 
mal  cavities  in  teeth  which  closely  approximate. 
XI.    The  thoroughness  or  lack  of  thoroughness  of  root- 
canal  fillings. 
XII.     Antrum  troubles  (roots  extending  into  or  foreign 
bodies  in  antrum). 

XIII.  Neuralgia,  exostosis,  and  hypertrophy. 

XIV.  Necrosis  (sequestra). 
XV.    Tumors. 

XVI.     Fractures  of  the  jaws. 

XVII.     Foreign   bodies   in    the    oesophagus,   larynx,   or 

bronchi,  resulting  from  accidents  during  dental 

operations. 

I.     In  recent  years,  through  the  influence  of  Angle  and 

others,  the  regulation  of   the  child's  teeth  is  undertaken 

much  earlier  than  when  the  old  maxim  obtained  of  waiting 

till  all  the  permanent  teeth  had  erupted.     The  diagnosis 

of  the  position  or    possible  non-existence  of  teeth  in  the 

maxilla?  of   young   subjects  is   of  vital   importance  to  the 

orthodontist.     The  .r-ray  is  of   inestimable  value  in  these 


THE  X-RAYS  OR  RONTGEN  RAYS 


187 


cases  as  a  means,  and  in  most  cases  as  the  only  means, 
of  accurately  determining  the  existing  conditions,  and  it  s 
not  an  exaggeration  to  say  that  without  it  in  many  cases 
treatment  would  better  be  postponed  until  the  eruption 
of  the  permanent  teeth. 

In  cases  of  impacted  teeth  the  determination  of  the 
angle  of  axial  deviation  from  the  proper  direction,  which 
prevents  the  eruption,  can  be  very  accurately  obtained  by 
means  of  a  radiograph.  Occasionally  more  than  one  view 
will  become  necessary  with  a  different  direction  of  rays. 
A  few  cases  have  occurred  in  the  writer's  practice  where 
the  simple  separation  of  the  two  teeth  adjoining  a  slightly 
impacted  one,  has  afforded  space  enough  for  the  latter  to 
erupt  easily. 


Fig.  S7 


Fig.  S8 


Fig.  87  shows  an  impacted  left  lower  second  bicuspid 
with  deciduous  second  molar.  After  extraction  of  the 
latter  and  separation  of  the  first  molar  and  first  biscupid 
the  tooth  assumed  its  normal  position,  Fig.  88. 

A  good  stereoscopic  skiagraph  is  often  of  considerable 
value  in  orthodontia,  but  although  good  work  is  being  done 
in  this  line,  there  is  still,  as  has  been  mentioned  before,  too 
much  diversity  of  opinion  as  to  the  proper  distance  at  which 
the  tubes  should  be  placed  at  each  side  of  the  median  line, 
to  enable  the  operator  to  follow  a  standard  method  of  ex- 
posure, and  thereby  obtain  reliable  results.  Figs.  S9  and 
90  show  an    impacted   right  upper  canine,  the  position  of 


188 


ELECT  RO-PH  YSICS 


which  appears  clearer  in  the  stereograph  than  in  the  single 
film.  The  arch  in  the  case,  when  widened,  and  the  lateral 
incisor  and  first  bicuspid  separated  will  allow  the  canine  to 
erupt  normally. 


Fig. 


Fig.  90 


Stereograph  of  right  upper  canine. 

Fig.  91  shows  impacted  upper  canine.  Figs.  92,  93,  and  94 
show  impacted  right  upper  canine  and  its  normal  position 
after  gaining  the  necessary  space  by  separation  of  the 
lateral  and  first  bicuspid. 


Fig.  91 


Fig.  92 


Impacted  canine. 


Impacted  right  upper  canine. 


Radiographs  taken  at  various  stages  during  the  process 
of  separating  the  two  teeth  adjoining  the  impacted  one  are 


THE  X-RAYS  OR  RONTGEN  RAYS 


189 


very  desirable  in  determining  the  necessary  force  to  be 
applied. 


Fig.  93 


Fig.  94 


During  separation.  Showing  space  provided. 

Fig.   95 


A  case  of  missing  tooth  germs. 


Cases  in  which  the  radiograph  has  shown  the  hopeless 
condition  of  missing  ncisors  and  canines  are  unfortunately 
not  rare. 


190 


ELECTRO-PHYSICS 


Fig.  95  shows  a  condition  of  two  missing  laterals  which 
relegates  the  case  from  the  orthodontist  to  the  mechanical 
dentist. 

II.  The  determination  of  the  length,  shape,  and  direction 
of  roots  for  crown  and  bridge  work  is  so  self-evident  that 
it  requires  no  further  remarks,  except  to  refer  the  reader  to 
Dieck's  methods  of  measurement  with  a  broach,  which  has 
been  already  described.     Fig.  96  shows  the  correct  direction 


Fig.  96 


Fig.  97 


Diagnosis  of  direction  of  canal. 


Result  of  not  diagnosing  by  x-ray. 


of  the  drill  in  preparing  the  root  for  a  pivot  tooth,  while 
in  Fig.  97  it  is  not  difficult  to  see  the  advantage  an  x-ray 
would  have  afforded  if  taken  while  fitting  the  post  of  the 
crown. 

In  cases  of  inflammation  of  the  tissues  surrounding  an 
impacted  lower  wisdom  tooth  which  presents  a  condition 
simulating  ankylosis,  and  making  extraction  necessary,  the 
shape  and  position  of  the  roots  of  the  teeth  may  become  of 
vital  importance,  and  here  again  the  .r-ray  is  of  inestimable 
value,  and  no  up-to-date  dentist  would  care  to  undertake 
such  extractions  without  obtaining  a  radiograph  as  a  guide 
in  operating. 

In  cases  in  which  the  operator  sees  a  possibility  of  such 
a  condition  in  his  patient's  mouth,  it  is  advisable  to  have  a 
radiograph  taken  while  the  condition  still  permits  of  the 
mouth  being  opened  and  the  film  inserted  comparatively 


THE  X-RAYS  OR  RONTOEN  RAYS 


191 


easily,  which  in  the  case  of  the  lower  wisdom  teeth  is  a 
proceeding  accompanied  by  considerable  discomfort  to  the 
patient  even  under  normal  conditions.  For  this  reason,  and 
especially  in  inflamed  conditions  of  the  angle  of  the  jaws, 
Heinz  Bauer  has  constructed  a  film-holder  wh  ch  the  writer 
has  found  indispensable  at  such  times.  The  film-holder 
consists  of  a  German-silver  case  of  suitable  size,  attached 
to  a  movable  handle.  After  inserting  the  film  the  case  is 
closed  by  an  aluminium  shutter  which  is  easily  penetrated 
by  the  rays,  offering  hardly  more  resistance  than  the  paper 
packing.  It  can  be  readily  sterilized,  and  forms  a  most 
important  part  of  the  dental  ar-ray  operator's  outfit. 


Fig.  98 


Film-holder. 


Tousey  speaks  of  a  film-holder  that  is  somewhat  similar 
in  shape,  but  the  ease  with  which  Bauer's  may  be  adjusted 
to  fit  either  side  of  the  mouth  seems  to  the  writer  a  great 
advantage. 

III.  Many  cases  of  absorption  of  the  apical  part  of 
roots  have  (before  Rontgen's  discovery)  proved  to  be  one  of 
the  greatest  disappointments  to  the  dentist.  Many  hours 
of  treatment,  a  burden  to  the  dentist  and  vexation  to  the 
patient,  might  have  been  spared  to  both  had  the  operator 
been  able,  as  he  is  now,  to  see  if  such  treatment  is  hopeless 
or  not.  The  writer  has  in  mind  a  case  which,  instead  of 
requiring  six  months  of  ineffectual  treatment  with  the  broach 
would  have  been  completed  in  one  sitting  with  the  forceps 


192 


ELECTRO-PHYSICS 


had  arrays  been  available.  Even  minute  degrees  of  ab- 
sorption may  be  the  cause  of  never-healing  fistulse  and  can 
easily  be  recognized  on  a  good  sharp  radiograph,  and  the 
tooth  doomed  to  extraction  or  root  amputation  without 
further  useless  treatment. 


Fig.  99 


Fig.  100 


Figs.  99  and  100.    Cases  of  absorption  in  connection  with 
alveolar  abscess. 


Fig.   101 


Fig    102 


The  value  of  root  amputation  has  been  proved  in  innumer- 
able cases  by  radiographs  taken  months  or  years  after  the 
operation. 


THE  X-RAYS  OR  RONTGEN  RAYS 


193 


Fig.  101  shows  left  upper  first  and  second  bicuspids  taken 
six  years  after  amputation  of  roots.  Both  teeth  firm  and 
surrounding  tissues  healthy. 


Fig.  103 


Fig.  104 


Fig.  102.  Case  of  fistula  of  right  upper  central  incisor, 
carrying  a  pivot-tooth,  and  accompanied  by  extensive  loss 
of  bone  structure.  Amputation  of  apex  was  resorted  to. 
Fig.  103  shows  end  of   root  lost  in  abscess  cavity  during 


Fig.  105 


Fig.  106 


operation.   Fig.  104  shows  condition  after  amputation.   Fig. 
105  case  a  year  and  a  half  after  operation.     The  cavity  has 
been  almost  entirely  replaced  by  newly  formed  bone. 
13 


194 


ELECT  RO-PE  YSICS 


Fig.  106.  Left  upper  first  molar  four  years  after  amputa- 
tion of  anterior  buccal  root;  tooth  firm  and  is  doing  good 
service. 

The  old  theory  that  the  roots  of  the  deciduous  teeth  are 
absorbed,  owing  to  the  pressure  upon  them  by  the  erupting 
permanent  teeth,  has  been  conclusively  disproved  by 
radiography.  For  many  arrays  have  shown  the  roots  of 
deciduous  teeth  to  be  partly  or  wholly  absorbed  without 
a  trace  of  a  permanent  tooth  under  them  to  which  this 
absorption  could  be  attributed. 


Fig.  107 


Fig.  108 


Fig.  107  represents  the  left  upper  deciduous  second  molar 
with  roots  nearly  wholly  absorbed  without  any  trace  of  a 
bicuspid  above  it. 

IV.  The  x-ray  has  proved  itself  to  be  of  inestimable  value 
in  the  diagnosis  of  the  extent  of  destruction  of  bone  as  a 
result  of  alveolar  abscess.  The  part  of  the  bone  destroyed 
by  the  abscess  absorbs  comparatively  little  of  the  rays,  so 
that  these  darken  the  corresponding  part  of  the  sensitive 
film  to  a  degree  more  or  less  marked,  according  to  the  size 
and  depth  of  the  abscess  cavity. 

Fig.  108  is  an  illustration  of  both  destruction  of  bone 
and  absorption  of  the  end  of  the  root  of  the  affected  molar. 

One  or  more  broaches  inserted  into  the  nerve  canal  and 
extending  through  the  apical  foramen  of  the  affected  roots 
will  often  show  the  operator  through  which  of  them  com- 
munication with  the  abscess  cavity  has  been  established. 


Fig.  109 


Fig.  110 


Abscess  on  lower  molar  showing  ex- 
tensive destruction  of  bone. 


Abscess-cavity  involving  upper 
canine  and  first  bicuspid. 


Fig.   Ill 


Fig.   112 


Broach  inserted  into  root-canal    and 
protruding  into  abscess-cavity. 


Connection  with  antrum  shown 
b3r  introduction  of  broach. 


Fig.   113 


A  case  of  fistula  opening  on  the  cheek  and  accompanied  by  considerable 
loss  of  bone. 


196 


EL  EC  TRO-PH  YSICS 


The  writer  has  at  times  seen  cases  of  marginal  abscess 
on  the  sides  of  the  roots  of  teeth  with  living  pulps;  these 
also  may  be  shown  on  the  radiograph. 

V.  The  presence  of  cysts  is  often  established  most  clearly 
by  means  of  .r-ray  diagnosis,  and  here  a  word  regarding 
the  differential  diagnosis  between  cyst  and  abscess  cavity  is 
necessary.     The  contour  of  the  abscess  cavity  is  more  or 

Fig.  114 


Cyst  in  mandible  containing  two  bicuspids  which  were  subsequently 
removed.  Radiograph  also  shows  impacted  second  molar  and  wisdom 
tooth  occupying  a  horizontal  position. 


less  diffuse  or  undefined,  the  cyst  generally  shows  a  sharp 
line  of  demarcation.  The  variety  of  cyst  in  question  is 
generally  the  radicular,  in  contradistinction  to  the  follicular; 
it  occurs  oftener  in  the  superior  than  in  the  inferior  maxilla. 
Radicular  cysts  are  generally  of  traumatic  origin  and  in 
many  cases  the  age  of  the  patient  at  the  time  of  the  acci- 
dent may  be  fairly  accurately  determined  by  the  degree  of 
arrested  development  of  the  root  and  the  size  of  the  canal, 


THE  X-RAYS  OR  RONTGEN  RAYS 


197 


if  the  accident  occurred  at  a  time  before  the  root  of  the 
tooth  in  question  was  fully  developed. 

The  approximate  date  of  lesions  of  a  traumatic  nature, 
resulting  in  pyorrhoea  or  absorption  may  be  established 
fairly  conclusively  by  the  z-ray.  Fig.  115  illustrates  a 
case  of  arrested  development  of  the  right  central  incisor 
which  shows  the  flaring  of  the  canal  at  the  apex,  causing 
slight  hemorrhage  upon  insertion  of  the  broach  and  inter- 
fering with  the  stopping  of  the  canal  with  gutta-percha. 
The  age  of  the  patient  at  the  time  of  the  accident,  according 
to  her  statement,  was  verified  by  the  radiograph. 


Fig.   115 


Fig.   116 


Showing  arrested  development  of  root. 


Showing  pyorrhoea. 


VI.  The  dentist  or  prophylactic  specialist  should  not  be 
satisfied  to  undertake  the  treatment  of  any  pronounced  case 
of  pyorrhoea  without  first  determining  by  jc-ray  diagnosis 
the  degree  of  destruction  of  the  alveolus  surrounding  the 
teeth  in  question,  and  should  compare  this  first  radio- 
graph with  one  or  two  taken  several  months  or  even  years 
after  treatment.  The  presence  of  calculus  on  the  roots  is 
also  in  many  cases  readily  discernible  on  a  good  x-ray  film, 
but  much  experience  in  the  selection  of  the  tube  and  in 
the  time  of  exposure  is  necessary  to  detect  this  in  every 
case,  whereas  the  amount  of  absorption  is  apparent  on  all 
but  the  very  poorest  films. 


19S 


ELECTRO-PHYSICS 


THE  X-RAYS  OR  RONTGEN  RAYS  199 

It  has  been  observed  that  in  many  instances  after  treat- 
ment of  pyorrhoea  the  condition  of  the  teeth  and  surround- 
ing tissues  has,  clinically  speaking,  greatly  improved;  that 
is  to  say,  the  flow  of  pus  has  stopped,  the  teeth  have  be- 
come firm,  the  pockets  closed  up,  and  the  gums  tightened 
around  the  roots;  still  the  radiograph  taken  at  this  time 
may  indicate  hardly  any  restoration  of  bone.  The  writer 
has  often  remarked  this  appearance  and  can  only  explain 
it  by  the  fact  that  prior  to  the  filling  up  of  spaces  by  new 
bone  structure  the  toned-up  connective  tissue  and  mucous 
membrane  forming  the  gum  substance,  cling  to  the  peri- 
cementum so  tightly  that  the  tooth  has  in  reality  become 
vastly  firmer  and  the  actual  formation  of  bone  does  not 
take  place  until  much  later.  This  condition,  however,  does 
not  show  on  the  radiograph,  probably  because  connective 
tissue  and  the  pus  ■  containing  pockets  shown  on  the  first 
film  present  approximately  the  same  degree  of  resistance 
to  the  .T-rays. 

A  radiograph,  taken  perhaps  for  an  entirely  different 
purpose,  occasionally  shows  a  tooth  apparently  hanging 
in  mid-air,  that  clinically  seems  comparatively  firm.  There 
seems,  however,  every  reason  to  assume  that  when  a  pyor- 
rhoea case  has  been  skilfully  and  successfully  treated,  restora- 
tion of  bone  around  the  roots  and  in  existing  pocket  cavities 
takes  place;  this  depends,  however,  on  the  age  of  the  patient 
and  the  severity  of  the  case. 

VII.  The  quest  of  the  dentist  who  has  never  had  a  broach 
or  drill  break  off  in  a  root-canal  would  have  afforded 
Diogenes  nearly  as  much  exercise  as  of  that  variety  of  man 
to  whose  discovery  he  devoted  so  much  energy  and  candle- 
grease;  and  as  there  are  unfortunately  very  many  cases 
in  which  such  a  broach-end  is  perfectly  innocuous,  if  sur- 
rounded by  chlora  and  gutta-percha,  it  is  only  necessary, 
in  order  to  quiet  or  disturb  the  operator's  mind,  to  determine 
by  an  a>ray  whether  the  broken-off  piece  is  entirely  con- 
tained in  the  canal  or  if  it  protrudes  through  the  apical 
foramen.  We  have  even  heard  of  cases  where  a  drill  has 
been  broken  off  and  sticks  out  at  the  side  of  the  root,  but 


200 


ELECTRO-PHYSICS 


as  it  is  always  "a  colleague"  who  has  perpetrated  this 
misdeed,  the  x-rsuy  dentist  can  await  the  development  of 
the   film   in    such   cases    philosophically. 

Fig.  119  shows  a  broken-off  root-canal  drill  perforating 
the  side  of  the  root. 


Fig.  119 


VIII.  Fractures  of  roots  can  readily  be  recognized  by 
radiographs.  These  should  in  all  cases  be  taken  after  any 
traumatic  lesion  to  teeth  or  jaws  and  can  often  save  the 
surgeon  or  dentist  much  time  and  trouble.  One  case  that 
occurred  in  the  writer's  practice  recently,  serves  to  illustrate 
this  fact  clearly.  An  officer  had  received  a  blow  against 
his  front  teeth  by  a  vigorous  toss  of  his  horse's  head.  The 
mesial  corner  of  the  left  central  was  broken  off  and  the 
right  one  was  fractured  so  that  the  labial  surface  was  split 
and  hung  only  by  a  piece  of  gum.  After  its  removal  the 
pulp  was  found  to  be  intact  and  not  exposed,  that  part  of 
the  tooth  being  apparently  as  firm  as  the  other  teeth.  In 
order  to  avoid  killing  the  pulp  it  was  decided  to  make  a 
platinum  cap  with  porcelain  facing,  and  this  was  set  and  no 
inconvenience  experienced  for  the  first  two  weeks.  But 
then  the  patient  returned  with  a  feeling  of  uneasiness  and 
looseness  of  the  cap,  which  made  an  x-ray  seem  desirable. 
This  showed  another  horizontal  fracture  about  6  milli- 
meters from  the  apex,  which  was  aggravated  by  the  cap, 
causing  the  two  parts  to  become  more  and  more  discon- 


THE  X-RAYS  OR  RONTGEN  RAYS  201 

nected,  and  ending  in  the  condition  described  above.  Now, 
the  root  upon  which  the  cap  was  cemented  seemed  per- 
fectly normal,  but  had  an  x-ray  been  taken  at  once,  both 
patient  and  operator  would  have  been  spared  much  trouble 
and  annoyance,  for  the  root  would  have  been  extracted  at 
the  beginning.  The  film,  though  plainly  revealing  the  con- 
dition described  above,  unfortunately  did  not  show  strong 
enough  contrasts  to  be  reproduced  here. 

IX.  The  existence  of  pulp  stones  may  be  demonstrated 
by  the  Rontgen  rays,  showing  as  a  body  of  approximately 
the  same  density  as  the  dentine,  and  occupying  a  part  of 
the  otherwise  dark-appearing  pulp  chamber.  These  pulp 
stones  are  by  no  means  always  apparent  and  it  requires 
much  experience  and  technique  in  choosing  a  tube  of  proper 
vacuum,  and  timing  the  exposure  correctly,  to  obtain  satis- 
factory results.  One  circumstance  should  not  be  over- 
looked, and  that  is  the  possible  presence  of  buccal  stoppings 
of  deceptive  size,  as  they  are  liable  to  dampen  the  operator's 
joy  on  considering  himself  the  happy  possessor  of  a  genuine 
pulp  stone  x-ray,  a  thing  of  comparatively  rare  occurrence 
in  the  practice  of  the  general  dental  practitioner  who  limits 
his  x-ray  work  to  his  own  practice. 

X.  One  of  the  most  discouraging  sights,  and  one  that 
unfortunately  occurs  in  the  best  of  practises,  is  that  of 
caries  under  crowns  and  caps  or  fillings  that  extend  under 
the  gum.  In  cases  of  suspected  approximal  cavities  in  very 
crowded  teeth  where  no  fillings  have  yet  been  inserted,  and 
which  could  hitherto  be  detected  only  by  wedging,  the 
writer  has  repeatedly  been  able  to  detect  caries  by  taking 
a  radiograph  of  two  or  more  of  the  teeth  in  question. 
Before  setting  any  gold  inlay  extending  well  under  the  gum, 
an  x-ray,  with  inlay  held  in  place,  should  always  be  taken 
and  will  save  much  trouble  in  smoothing  away  "catches" 
subsequently. 

XL  The  determination  of  the  degree  of  perfection  attained 
in  root-canal  filling  is  another  field  for  the  x-ray  and  one 
which  does  not  always  afford  an  unalloyed  pleasure  to  the 
operator,    no  matter  how  conscientious  he  may  be  in  his 


202 


ELECTRO-PHYSICS 


work,  for  what  dentist  has  not  had  the  experience  of 
occasionally  having  failed  to  fill  a  canal  to  the  apex,  which 
without  the  detective  x-ray  would  have  satisfied  his  con- 
science entirely?  It  will  certainly  help  to  show  up  the 
operator  "who  always  succeeds  in  filling  every  root  canal 
to  the  very  apex,  no  matter  how  small  or  crooked  it  is." 
On  the  other  hand,  the  x-ray  has  that  comforting  feature 
in  that  it  shows  that  an  innumerable  quantity  of  roots 
treated  by  conscientious  and  skilful  men  have  not  been 
filled  to  the  apices,  but  are,  so  far  as  we  can  judge,  doing 
as  well  as  if  this  ideal  had  been  possible  of  attainment. 
This  is  not  meant  as  a  plea  for  careless  root-canal  filling, 


Fig.   120 


Fig.  121 


Fig.   122 


Figs.  120  to  122. — Caries  under  caps  and  old  stoppings. 

but  to  show  that  where  manual  skill  fails  to  accomplish  the 
impossible,  nature  often  takes  care  of  things  herself.  The 
writer  certainly  considers  it  more  advisable  to  treat  minute 
remnants  of  nerve  filaments  in  roots  found  by  the  radiograph, 
to  be  curved,  as  a  negligible  quantity,  after  having  sterilized 
them  as  well  as  possible,  than  to  run  the  risk  of  drilling 
through  the  side  with  a  Gates-Glidden  or  Beutelrock  root- 
canal  drill.  The  fact  that  gutta-percha  as  a  root-canal  filling 
is  most  desirable  has  also  been  proved,  it  would  seem  con- 
clusively, by  the  x-ray,  for  the  writer  has  in  several  cases 
seen  how  kindly  nature  takes  to  it  even  when  it  has  been 
pushed  through  the  apex,  as  appears  in  Fig.  123.  In  this 
case  the  root-filling  of  the  canine  that  had  been  inserted 


THE  X-RAYS  OR  RONTGEN  RAYS 


203 


six  or  seven  years  previously,  was  not  the  cause  of  the 
taking  of  the  radiograph,  the  gutta-percha  not  having 
caused  the  slightest  inconvenience. 


Fig.  123 


Fig.   124 


Gutta-percha  extending  through 
apex. 


Absorption  of  root  and  gutta- 
percha protruding. 


Fig.  124  shows  extensive  absorption  of  the  end  of  left 
upper  canine  root.  The  protruding  part  of  the  gutta- 
percha root-canal  stopping  has  evidently  assumed  a  nearly 
horizontal  position. 

XII.  In  affections  of  the  antrum  the  .r-rays  often  form 
an  important  link  in  the  chain  of  diagnostic  factors, 
and  a  radiograph  should  certainly  be  taken  if  there  remains 
any  doubt  after  illuminating  the  oral  cavity  and  resorting 
to  the  usual  means  of  diagnosis.  The  radiograph  should  be 
taken  with  a  large  plate  postero-anteriorly,  the  face  of  the 
patient  firmly  pressed  against  it,  and  the  exposure  should 
be  shortened  by  the  use  of  a  good  intensifier.  The  tube 
should  have  a  resistance  of  13  to  15  Wehnelt  or  9  to  10 
Bauer  qualimeter.  Empyema  of  the  antrum  will  be  indi- 
cated by  a  lighter  appearance  of  the  affected  side,  as  the 
rays  will  be  absorbed  more  readily  by  the  pus-containing 
secretions.  There  are,  however,  so  many  cases  in  which 
the  density  of  normal  bone  may  vary  considerably  on 
either  side,  that  the  radiograph  alone   should  not  be  con- 


204 


ELECT  RO-PH  YSICS 


sidered  sufficient.  Fig.  125  shows  a  case  of  empyema  of 
the  right  antrum  and  frontal  sinus.  The  affected  antrum 
appears  darker  on  the  print  owing  to  the  absorption  of 


Fig.  125 


the  rays  by  the  pus-containing  fluids.  On  the  primary 
plate,  of  course,  the  appearance  is  reversed.  The  patient 
had  not  removed  her  artificial  dentures. 

A  skiagraph  may  also  be  taken  with  a  large  film  or  plate 


THE  X-RAYS  OR  RONTGEN  RAYS 


205 


in  the  mouth  held  between  the  teeth,  the  rays  being  directed 
from  above,  but  the  presence  of  the  bicuspids  and  molars 
is  likely  to  preclude  a  clear  image  of  the  parts  in  question. 
Should  the  upper  jaw,  however,  be  edentulous,  or  at  any 
rate  as  far  as  molars  and  bicuspids  are  concerned,  the 
radiograph  taken  in  this  manner  and  showing  at  least  a 
part  of  the  antrum  of  each  side,  may  be  a  very  valuable 
help  to  diagnosis.  The  presence  of  roots,  dentigerous 
cysts,  or  even  foreign  bodies  in  the  antrum  may  of  course 
be  easily  demonstrated  in  this  way.  Dieck  reports  a  case 
in  which  a1  bicuspid  root  was  forced  up  into  the  antrum 
during  an  extraction.  In  this  connection  it  will  be  well  to 
bear  in  mind  the  possibility  of  misinterpretation  referred  to 
before,  which  may  be  brought  about  by  the  inclusion  of 
the  root-ends  on  the  film  within  the  image  of  the  antrum, 
while  the  root  itself  may  occupy  its  normal  position  in  the 
maxilla. 

Fig.  126 


XIII.  The  subject  of  facial  neuralgia  is  one  that  extends 
into  so  many  different  territories  that  its  thorough  con- 
sideration is  of  course  out  of  the  question  here.  Suffice 
it  to  say  that  its  origin  is  often  of  so  obscure  a  nature, 
while  the  trouble  itself  may  become  a  source  of  intense 
agony  to  the  patient,  that  no  possible  aid  to  its  diagnosis 
should  be  neglected,  and  an  z-ray  may  reveal  conditions 
(chiefly  of  impacted  teeth)  the  removal  of  which  may 
restore  health  and  comfort  to  the  sufferer.  Fig.  126  shows 
an  impacted  left  lower  second  bicuspid  pressing  against 
the  first   molar  root   and   causing  absorption  and   all  the 


206 


ELECT RO-PE  YSICS 


symptoms  of  severe  neuralgia.  The  patient  has  experienced 
no  more  trouble  since  the  extraction  of  the  molar.  Upson, 
among  others,  strongly  urges  the  radiographic  examination 
of  the  jaws  and  teeth  of  all  patients  suffering  from  mental 
disorders,  even  if  no  direct  indication  of  their  dental  origin 
is  apparent.1  Exostosis  of  roots  is  also  one  of  the  causes  of 
neuralgia  which,  before  the  era  of  the  Rontgen  ray,  were 
a  source  of  the  greatest  difficulty  to  the  diagnostician, 
often  leading  to  the  extraction  of  one  tooth  after  another 
until  the  exostosed  ones  were  revealed  and  removed, 
whereas  now  an  x-ray  easily  shows  us  the  seat  of  the 
trouble.  Osseous  deposits  on  the  wall  of  the  pulp-chamber 
causing  pressure  on  the  pulp  are  also  often  detected  by 
the  Rontgen  film.  Fig.  127  shows  exostosis  on  roots  of  both 
bicuspids,  also  an  ill-fitting  cap  on  first  molar. 

Fig.  127 


XIV.  Necrosis  in  its  different  stages  affords  the  x-ray 
an  opportunity  of  proving  its  value  as  a  diagnostic  factor. 
At  first,  according  to  Pfahler,  a  transparent  condition  of 
the  bone  is  apparent,  owing  to  the  disturbance  of  the  fine 
net-work  of  cancellous  structure  caused  by  lack  of  nutrition, 
brought  about  by  the  destruction  of  bony  elements.  The 
sequestrum,  which  on  the  film  appears  light,  surrounded  by 
a  dark  area  of  decalcified  bone,  is  usually  easily  recognized 
and  its  location  and  removal  is  thus  facilitated. 

XV.  For  the  diagnosis  of  tumors  the  Rontgen  rays 
have  been  used  in  many  instances  with  success,  and  al- 

1  Dental  Cosmos,  May,  1910,  p.  525;  May,  1912,  p.  954. 


THE  X-RAYS  OR  RONTGEN  RAYS  207 

though  the  dentist  would  naturally  not  be  very  conversant 
with  the  differential  diagnosis  of  these  dangerous  diseases, 
the  appearance  of  a  certain  transparency  of  the  bone  on 
the  photographic  film  may  serve  to  arouse  his  suspicions 
and  determine  him  to  call  in  a  pathologist  or  surgeon 
while  there  is  still  a  possibility  of  successful  operation. 
Pfahler  says:1  "Tumors  of  the  lower  maxilla  are  shown 
by  a  disturbance  in  the  cancellous  tissue,  at  first  consisting 
merely  of  an  absorption  of  the  calcium  salts,  resulting  in  a 
greater  transparency,  then  followed  by  more  complete 
destruction.  This  disease  is  not  as  definitely  outlined  as 
in  necrosis,  fading  gradually  into  healthy  bone,  and  is 
often  associated  with  the  formation  of  new  tissue.  Car- 
cinoma seems  to  cause  more  destruction  of  bone  and  less 
new  tissue  than  sarcoma.  Most  of  the  primary  tumors 
seem  to  be  sarcoma,  but  the  metastatic  are  most  likely  to 
be  carcinoma.  Not  only  the  character  but  the  extent  of  the 
disease  may  thus  be  determined,  and  thus  material  assist- 
ance be  secured  in  outlining  treatment."  In  differentiating 
between  exostosis  and  malignant  bony  growths,  Shenton2 
emphasizes  the  regularity  and  uniformity  of  the  former  in 
contrast  to  the  ragged  and  spotty  appearance  of  the  latter. 

XVI.  Fractures  of  the  jaws  also  offer  a  field  of  useful- 
ness for  the  radiograph  which  should  be  welcomed  by  the 
dental  surgeon.  Prior  to  the  adoption  of  any  treatment, 
an  .-r-ray  should  be  taken  to  indicate  the  proper  course 
to  be  pursued;  whether  a  splint  or  wire  ligature  should  be 
applied  and  in  the  latter  case  where  the  bone  is  strong- 
enough  to  be  perforated  so  as  to  introduce  the  wire.  Ac- 
cording to  Pfahler,  fractures  of  the  jaws  are  liable  to  occur 
at  the  places  weakened  by  an  extensive  abscess  cavity, 
which  again  affords  the  liability  of  infection  to  the  fractured 
area.  The  radiograph  shows  at  first  a  dark,  irregular  line 
on  the  film,  followed  in  later  exposures  by  the  gradual 
disappearance  and  the  formation  of  normal  bone.  Non- 
union is  of  course  also  apparent  on  the  film,  and  is  indicated 

1  Dental  Cosmos,  September,  1911,  p.  1084. 

2  "Disease  in  Bone  and  its  Detection  by  the  X-rays,"  1911,  pp.  64,  68. 


208  ELECTRO-PHYSICS 

by  the  persistence  of  the  dark  area  and  the  formation  of 
sequestra. 

XVII.  When  one  considers  the  number  of  cases  in  which 
the  dentist,  especially  one  occupying  himself  largely  with 
crown  and  bridge  work,  may  experience  the  pang  of  sud- 
denly seeing  a  band  or  post  disappearing  down  the  throat 
of  his  patient,  one  can  only  wonder  at  the  comparatively 
few  instances  recorded.  But  if  it  be  only  once  in  a  lifetime, 
it  is  enough  to  make  the  dentist  thankful  for  possessing 
an  x-ray  outfit,  if  for  no  other  purpose  than  to  be  able  to 
locate  the  object  so  as  to  facilitate  its  removal  before  it 
is  too  late.  A  surgeon  with  the  necessary  instruments 
should  be  summoned  so  as  to  be  at  hand  when  the  plate 
has  been  developed. 

A  few  writers  have  advocated  the  injection  of  a  paste 
composed  of  bismuth  and  paraffine  into  fistulse  and  abscess 
cavities,  so  as  to  show  them  in  greater  contrast  on  the  film, 
but  the  writer  considers  that  as  this  paste  approximates 
bone  tissue  so  nearly  in  point  of  density,  but  little  is  gained 
by  its  use. 


B. 

The  therapeutic  value  of  x-rays  in  dentistry  is,  up  to  the 
present  date,  largely  speculative,  and  while  Tousey  claims 
marked  improvement  in  many  cases  of  pyorrhoea  when 
treated  by  a  combination  of  high-frequency  and  arrays 
with  a  tube  especially  constructed  by  him  (after  thorough 
instrumentation),1  there  still  seems  too  large  an  element 
of  danger  in  it  to  recommend  this  treatment  to  the  inex- 
perienced operator. 

Tousey  also  mentions  one  case  of  necrosis  with  fistula 
penetrating  into  the  nose,  which  healed  a  couple  of  weeks 
after  x-ray  exposures  were  made.2  The  writer  has  also 
noted  a  few  cases  of  severe  periodontitis  which  showed 
marked  improvement  after  radiographs    were    taken,  but 

1  Tousey,  pp.  566-7.  2  Ibid.,  pp.  806-7. 


THE  X-RAYS  OR  RONTGEN  RAYS  209 

it  is  difficult  to  prove  that  the  Rontgen  rays  were  actually 
the  healing  factors.  In  case  of  obstinate  pericementitis 
in  which  the  ordinary  remedies  do  not  yield  relief,  one  or 
two  exposures  of  20  to  40  seconds  according  to  the  strength 
of  the  current  and  the  severity  of  the  case  should  by  all 
means  be  tried.  Dr.  C.  F.  Boedeker,  of  Berlin,  has  been 
experimenting  with  this  mode  of  treatment  for  a  year  or 
more,  and  will  shortly  publish  his  experiences,  which  bid 
fair  to  be  of  great  interest  to  the  profession.  The  future 
will  certainly  open  up  further  fields  of  usefulness  for  the 
.r-ray  as  a  therapeutic  agent  in  denta  and  oral  medicine. 
While  it  is  far  better  than  nothing,  of  course,  to  be  able 
to  send  one's  patient  to  the  .r-ray  specialist  to  obtain  a 
dental  film  or  plate,  the  advantage  to  the  dentist  of  having 
his  own  outfit  and  being  able  to  work  it  as  he  pleases,  is 
so  great  that  he  who  has  once  possessed  one  would  never 
want  to  give  it  up  again.  For,  in  the  first  place,  even  a 
dental  a*-ray  specialist  could  not  always  know  what  was 
desired  unless  it  were  pointed  out  to  him  in  the  mouth  of 
the  patient.  Then  the  fact  of  having  to  send  the  patient 
away  after  first  making  an  appointment  with  the  specialist, 
is  enough  to  limit  the  taking  of  a  radiograph  to  the  most 
important  cases,  whereas  the  possession  of  one's  own  outfit 
is  such  a  convenience  to  both  patient  and  dentist  that 
the  advantage  is  obvious.  There  are  many  men  who  con- 
sider that  the  time  is  near  at  hand  when  no  root  treatment 
will  be  considered  entirely  up-to-date  without  two  or  three 
.r-rays  taken  in  the  course  of  the  same,  as  a  guide  to  the 
operator;  and  in  crown  and  bridge  work  the  advantage  of 
frequent  radiographs,  showing  the  direction  of  the  pivot 
and  its  permissible  length,  is  self-evident.  If  the  radio- 
graph is  worth  having  (which  is  indisputable),  and  if  it 
can  be  in  the  dentist's  hands  inside  of  five  minutes  (for 
the  inspection  in  the  fixer  is  to  be  recommended  as  well  as 
after  it  has  been  fixed),  it  is  worth  the  dentist's  while  to  go 
to  the  expense  and  trouble  of  having  the  work  done  in  his 
own  surgerv. 


14 


PART  II. 
ELECTRO-THERAPEUTICS. 


CHAPTER  VIII. 
ELECTRO-PHYSIOLOGICAL  EFFECTS. 

General  Considerations — Conduction  by  Ions. 

General  Considerations. — Research  of  a  purely  physiological 
nature  has  demonstrated  the  existence  of  electrical  manifes- 
tations in  animals.  Differences  of  potential  of  the  surface 
of  the  body  are  always  present  and  may  be  detected  by 
delicate  electrometric  methods.  Electrical  manifestations 
are  especially  noticeable  in  some  species  of  fish,  greatest 
of  all  in  the  electric  eel  and  the  torpedo,  which  yields  elec- 
trical discharges  of  considerable  magnitude.  Electric  cur- 
rent is  especially  noticeable  in  muscle  and  nerve  tissue, 
but  it  has  been  stated  that  it  is  to  be  found  in  all  tissues 
of  the  body.  This  phenomenon  has  been  tested  with 
delicate  galvanometers  especially  constructed  for  the  pur- 
pose, and  non-polarized  electrodes.  The  skin  has  been 
stated  to  possess  a  current  after  it  has  been  removed  from 
the  body  (as  for  grafting),  by  placing  a  non-polarizing 
electrode  on  the  inner  side  and  a  delicate  galvanometer 
in  circuit  with  another  electrode  on  the  outer  side,  as  long 
as  vitality  exists  a  weak  current  will  pass  from  the  greater 
potential  on  the  inner  side  to  the  outer.  The  healthy  skin 
has  also  been  shown  to  possess  currents  which  can  be 
excited  and  will  flow  toward  the  portion  which  is  negative 


212  ELECTRO-THERAPEUTICS 

to  the  greater  potential.  Exertion  of  the  brain  and  con- 
traction of  muscle  produce  currents  which  can  be  detected 
by   the   use   of   electrometric   instruments. 

The  electrical  currents  which  occur  in  muscles  and 
nerves  are  of  a  continuous  kind  when  in  repose,  and  inter- 
mittent when  in  activity.  Physiological  experiments  have 
been  performed  on  fresh  living  muscle  and  nerves  which 
demonstrate  this  phenomenon,  but  it  has  been  stated  that 
the  continuous  electric  current  flows  as  an  effect  of  artificial 
condition  produced  by  removal  of  the  tissues  from  the  body. 
The  intermittent  current  can  be  produced  by  stimulating 
the  tissue,  when  a  current  will  flow  at  each  contraction. 

Conduction  by  Ions. — In  the  living  body  when  a  con- 
tinuous current  is  applied  it  is  conducted  by  the  tissues  of 
the  body  from  one  point  of  contact  to  the  other  as  if  the 
conduction  were  through  a  liquid,  the  body,  as  has  been 
stated,  being  an  electrolyte,  the  current  is  conveyed  by 
charges  which  are  imparted  to  the  ions » contained  in  the 
tissues.  Lewis  Jones1  describes  this  process  as  follows: 
"Conduction  in  watery  solutions  of  salts  (and  the  tissues 
of  the  body  may  be  regarded  as  coming  into  this  category) 
take  place  only  by  the  conveyance  or  transport  of  charged 
particles  or  'ions'  through  the  liquid  from  one  metallic 
terminal  to  the  other,  and  without  this  movement  of  ma- 
terial particles  there  is  no  conduction  in  liquid  solutions. 
The  moving  particles  or  ions  are  the  result  of  the  dis- 
sociation of  the  molecules  of  the  salts  by  the  process  of 
solution,  so  that  a  solution  of  sodium  chloride  in  water 
contains  abundance  of  dissociated  ions  of  chloride  carrying 
negative  charges  and  of  sodium  carrying  positive.  When 
a  current  is  applied  there  is  a  double  movement  among  the 
ions — a  procession  of  the  chlorine  ions  to  the  positive  pole 
and  of  the  sodium  ions  to  the  negative,  every  ion  carrying 
its  appropriate  positive  or  negative  charge,  so  that  the 
measurement  of  the  current  by  a  galvanometer  in  the  cir- 
cuit gives  an  accurate  indication  of  the  number  or  amount 

1  Medical  Electricity,  p.  300. 


CONDUCTION  BY  IONS  213 

of  the  chlorine  ions  brought  to  the  positive  pole  and  of  the 
sodium  ions  brought  to  the  negative." 

This  transfer  of  the  current  by  charging  of  the  ions  in 
both  directions  constitutes  an  important  factor  in  the 
ionic  effect  of  the  current,  that  electro-positive  ions  move 
in  their  particular  direction  while  at  the  same  time  electro- 
negative ions  move  in  the  opposite  direction  should  not 
be  lost  sight  of. 

When  metallic  electrodes  are  applied  to  the  surface  of 
the  body,  a  migration  of  ions  occurs  at  both  poles  from  the 
surface  of  the  electrode  (metallic  ions  enter  from  the  posi- 
tive pole)  for  this  reason  at  the  site  of  contact  of  the  electrode, 
where  ions  are  often  not  desired,  great  caution  should  be 
exercised  to  prevent  the  entry  of  deleterious  ions  from 
the  metal  or  liquid  electrode  into  the  body  at  that  point. 
Electrodes  should  be  covered  with  some  protecting  material 
like  chamois  skin  or  lint  which  should  be  kept  scrupulously 
clean;  if  the  metal  be  brought  in  contact  with  the  skin 
destruction  of  the  tissue  might  occur  by  the  transfer  of 
ions  either  from  the  metal  or  from  salts  in  the  tissues  at 
the  point  of  contact,  this  will  be  manifest  by  a  blister  or 
destruction  of  a  tissues,  a  caustic  effect,  similar  to  that 
produced  by  plunging  a  metallic  electrode  into  tissue  for 
destruction  of  hair  follicles  and  usually  referred  to  as  electro- 
lysis. Leduc  in  referring  to  this  effect  of  the  passing  of 
the  current  between  electrodes  applied  to  the  tissues  of 
the  body  says:  "The  electrodes  employed  for  medical 
application  of  electric  current  are  either  insensitive  elec- 
trodes— carbon,  platinum,  etc. — or  sensitive  electrodes — 
zinc,  copper,  etc. — or  electrolytic  electrodes  formed  of 
aqueous  solutions  of  salts,  acids,  or  bases.  In  the  case  of 
the  insensitive  electrode,  the  anions,  after  having  given 
up  their  charges  at  contact  with  the  anode,  become  anhy- 
drides, which,  in  order  to  make  the  corresponding  acids, 
carry  off  hydrogen  from  the  tissues  which  they  destroy — 
2Cl+H20  =  2HCl+0— and  oxygen  is  liberated." 

The  kations,  after  contact  with  the  kathode,  take  the 
chemical  character  of  the  alkali  metals,  and  carry  off  the 


214  ELECTRO-THERAPEUTICS 

hydroxy  1  group  from  the  tissue,  which  they  destroy,  freeing 
hydrogen:  K+H20  =  KOH+H.  If  we  employ  electrodes 
which  can  be  acted  on  by  the  products  of  electrolysis,  the 
phenomena  at  the  anode  consists,  firstly,  of  the  formation 
of  acid,  with  the  destruction  of  the  tissue,  and  then  the 
attack  and  dissolution  of  the  electrode  by  the  acid  formed. 
From  this  there  results  a  salt  of  the  metal  of  the  electrode 
which  gives  rise  to  the  phenomena  presented  by  the  elec- 
trolytic electrodes.  When  we  use  as  electrodes  electrolytes 
— i.  e.,  solutions  of  salts  acids  or  bases — there  is  produced 
by  the  passing  of  the  current  an  exchange  of  ions  between 
the  body  and  the  electrodes.  At  the  anode  the  body  gives 
up  its  anions  and  receives  the  kations  of  the  electrode;  at 
the  kathode  the  body  gives  up  its  kations  and  receives  the 
anions  of  the  electrode." 

These  effects  produced  in  the  body  by  the  passing  of 
the  current  are  identical  with  the  electrolytic  effects  pro- 
duced in  a  cell  or  other  electrolyte  as  already  described. 
The  ion  itself  may  be  an  invisible  product  of  electrolysis, 
the  presence  of  which  cannot  be  detected  except  by  its 
effect  on  the  tissue  of  the  body  or  by  a  secondary  chemical 
combination  by  which  it  is  transformed  into  a  new  product 
which  can  be  seen.  The  movement  of  ions  from  the  sur- 
face of  metallic  electrodes  in  an  electrolyte,  the  rapidity 
with  which  they  are  formed,  and  their  direction  of  pene- 
tration was  demonstrated  by  the  author  in  an  experiment 
before  the  Odontological  Section  of  the  Royal  Society  of 
Medicine  (vol.  v,  pp.  102),  1912.  Metal  electrodes  of  the 
same  area  and  cross-section  as  those  used  by  him  in  actual 
practice  for  the  treatment  of  pyorrhoea  alveolaris  were 
used  for  the  experiment,  which  was  performed  as  an  ocular 
demonstration  of  the  small  amount  of  current  strength 
required  to  instantaneously  produce  a  movement  of  ions 
from  soluble  electrodes.  To  quote  the  experiment  from 
the  proceedings  of  the  Royal  Society  of  Medicine,  vol.  v, 
1912. 

"I  have  here  two  glass  tubes,  each  G  cm.  long  and  1  cm. 
in  diameter,  open  at  both  ends,  these  tubes  are  filled  with 


(  nXDUCTIOX  BY  IOXS 


215 


coagulated  albumen.  In  one  tube  the  albumen  has  been 
mixed  with  a  trace  of  ferricyanide  of  potassium,  the  other 
contains  pure  albumen.  The  tubes  are  placed  side  by  side 
standing  on  the  small  platform,  which  has  a  platinum 
electrode  connected  by  wire  to  the  thumbscrew,  to  which 
is  attached  the  negative  lead  wire;  the  other  ends  are  in 
contact  with  a  similar  electrode  which  is  connected  with 
the  other  thumbscrew,  to  which  is  attached  the  positive 
lead  wire.      The  albumen  is  the  electrolyte,  which,  being 

Fig.   12s 


Ferrous  and  copper  ions  in  albumen. 


white,  readily  shows  the  movement  of  ions  as  they  take 
place.  Two  lengths  of  iron  wire,  each  2  cm.  long  and  1  mm. 
thick,  are  placed  one  on  each  end  of  the  glass  tube  con- 
taining the  mixture  of  albumen  and  ferricyanide  of  potas- 
sium, passing  along  the  side  of  the  glass  so  that  they  are 
readily  seen,  the  ends  of  the  wire  are  bent  over  the  sides 
of  the  glass  and  are  in  contact  with  the  platinum  electrodes. 
A  similar  arrangement  is  carried  out  with  copper  wire  in 
the  other  glass  tube  which  contains  pure  albumen. 

The  reason  for  mixing  ferricyanide  of  potassium   with 


216  ELECTRO-THERAPEUTICS 

the  albumen  in  the  tube  in  which  is  placed  the  iron  wire  is 
that  ferrous  ions  are  invisible,  but  when  brought  in  con- 
tact with  ferricyanide  of  potassium,  Prussian  blue  is  formed. 
Iron  and  copper  are  both  soluble  electrodes,  and  when  a 
current  of  about  5  ma.  is  passed  you  can  see  ferrous  ions 
and  copper  ions  migrate  from  the  surface  of  the  metals, 
the  ferrous  ions  staining  the  albumen  a  Prussian  blue  and 
the  copper  ions  a  light  green ;  this  takes  place  at  the  positive 
pole.  At  the  negative  pole  no  change  takes  place  except 
the  formation  of  hydrogen  gas.  I  would  draw  your  attention 
particularly  to  the  rapidity  with  which  the  ions  are  formed 
and  the  depth  of  penetration." 

The  effect  produced  by  the  passing  of  the  current  through 
this  electrolyte  demonstrates  some  of  the  changes  which 
actually  take  place  in  ionic  medication.  Much  more  con- 
clusive experiments  have  been  carried  out  by  Dr.  N.  S. 
Finzi,1  of  London,  with  a  view  to  determining  the  path 
which  ions  take  when  introduced  into  the  living  tissues. 
The  experiments  were  performed  on  cats,  rabbits,  a  monkey, 
and  a  dog.  A  number  of  various  ions  were  introduced  into 
the  tissues  of  the  animals  by  ionic  medication,  the  tissues 
containing  the  ions  were  removed,  and  the  ions  stained  in 
situ  by  saturating  the  tissues  with  a  chemical  which  caused 
a  colored  compound  with  the  ions.  The  results  of  these 
experiments  are  of  great  practical  importance  in  showing 
conclusively  the  great  depth  of  penetration  of  some  ions. 
To  quote  one  of  these  experiments  as  published  in  the 
British  Medical  Journal: 

"A  monkey  was  anesthetized  by  chloroform  and  a  pad 
soaked  in  potassium  ferricyanide  was  placed  over  the  front 
of  its  knee,  the  area  which  the  solution  touched  being 
limited  by  a  window  cut  in  a  piece  of  oil-silk.  This  pad  was 
connected  with  the  negative  pole,  that  attached  to  the 
positive  pole  being  placed  on  the  back.  A  current  of  10 
milliamperes  was  passed  for  thirty  minutes,  and  then  the 
animal  was  killed.     Before  its  death,  however,  the  knee 

1  British  Medical  Journal,  November  2,  1912. 


CONDUCTION  BY  IONS  217 

was  removed  by  cutting  through  the  thigh  and  the  leg, 
and  was  placed  in  a  solution  of  ferrous  sulphate.  A  con- 
trol experiment  was  performed  in  which  a  pad  of  potassium 
ferricyanide  was  fixed  on  a  monkey's  knee  for  the  same 
length  of  time,  no  current  being  passed,  and  the  knee  was 
subsequently  treated  in  the  same  way.  The  next  day 
the  knee  was  opened,  and  it  was  found  in  the  case  in  which 
the  current  was  used  that  the  skin,  subcutaneous  tissues, 
and  patellar  tendon  over  which  the  window  had  been 
placed  were  stained  an  intense  blue  from  the  interaction  of 
the  ferricyanide  ions  and  the  ferrous  sulphate,  and  further 
that  this  blue  extended  right  into  the  joint,  there  being 
a  stained  patch  on  the  cartilage  which  penetrated  right 
down  to  the  bone.  In  the  control  the  blue  did  not  even 
penetrate  the  skin.  This  definitely  proves  that  it  is  possible 
to  introduce  the  ions  of  some  substances  directly  into  a 
joint,  even  into  the  cartilages;  at  any  rate  of  a  compara- 
tively superficial  joint  like  the  knee." 

This  experiment  is  one  of  many  performed  by  Dr.  Finzi 
which  were  quite  as  convincing  but  it  is  quoted  to  show 
that  penetration  of  ions  takes  place  equally  well  at  the 
cathode  as  at  the  anode  of  a  solution  if  the  acid  radicle  type 
is  applied  with  the  intention  of  driving  in  that  particular 
ion,  it  is  probably  one  of  the  most  conclusive  experiments 
in  this  direction  yet  published. 

Copper  electrodes  are  often  used  by  the  author  for 
ionization  of  fistulous  tracts  in  cases  of  chronic  alveolar 
abscess.  It  is  precisely  the  same  effect  as  described  by 
W.  J.  Morton1  under  the  title  of  "Cataphoric  Medication 
or  Electric  Medicamental  Diffusion,"  in  which  he  states 
that  "by  cataphoretic  medication  we  mean  the  specific 
introduction  of  drugs  or  medicaments  into  living  tissue; 
this  may  be  done  in  two  ways,  viz.,  by  employing  solutions 
in  contact  with  non-oxidizable  electrodes  or  by  employing 
electrodes  which  are  attacked  by  the  chemicals  formed  at 
either  pole  by  the  action  of  the  current  upon  the  fluids  of 

1  Cataphoresis,  p.  150. 


218  ELECTRO-THERAPEUTICS 

the  tissue  and  upon  the  electrodes."  The  second  of  these 
methods  produces  what  he  described  as  electric  diffusion 
but  which  is  more  often  spoken  of  as  the  ionic  effect;  for 
many  reasons  it  is  unfortunate  that  the  cataphoric  and  the 
electric  diffusion  effects  were  so  closely  linked  together  by 
Morton. 

Guilleminot1  referring  to  this  "polar"  action  of  oxidizable 
metallic  electrodes  states:  "When  the  electrode  is  made  of 
an  oxidisable  metal,  the  acids  set  free  at  the  anode  attack 
the  metal,  forming  salts  which  act  as  electrolytes,  thus 
producing  the  so-called  tertiary  effects."  And  again,  re- 
ferring to  this  action  when  electrolytic  solution  is  employed 
as  an  electrode,  he  says:  "At  the  anode  there  is  a  stream  of 
anions  passing  out  of  the  body,  while  a  stream  of  cathions, 
furnished  by  the  electrode,  traverses  the  integuments  and 
penetrates  the  body.  At  the  cathode  a  stream  of  cathions 
leaves  the  body  while  the  anions  of  the  electrode  pass  into 
it." 

Leduc  demonstrated  the  penetration  of  ions  into  the 
body  by  using  colored  ions.  He  points  out  that  if  a  solution 
of  permanganate  of  potash  be  employed  on  both  arms  and 
current  passed,  the  ions  stain  the  tissue  at  the  negative 
electrode,  a  brown  punctate  rash  appearing  at  that  pole, 
while  at  the  positive  pole  no  such  staining  takes  place. 
The  effect  on  the  system  he  demonstrated  by  employing 
sulphate  of  strychnine  with  a  positive  electrode  applied 
to  the  inner  surface  of  the  ear  of  a  rabbit.  If  no  current 
be  passed  the  strychnine  solution  can  stay  indefinitely  in 
position  without  any  effect,  but  b}r  passing  a  current  tetanic 
convulsions  typical  of  strychnine  poisoning  causes  the  death 
of  the  rabbit. 

The  author  once  saw  a  patient  suffer  from  alarming 
toxic  effects  of  cocaine  under  the  following  circumstances: 
The  patient,  a  powerful  man,  had  an  incisor  fractured 
and  the  pulp  exposed;  in  order  to  anesthetize  the  pulp  a 
pellet  of  cotton-wool  soaked  in  a  20  per  cent,  solution  of 

1  Electricity  in  Medicine,  p.  197. 


CONDUCTION  BY  IONS  219 

cocaine  was  placed  on  it  and  a  platinum  electrode  applied 
to  this  conveying  positive  electricity,  the  negative  electrode 
was  held  in  the  hand.  The  current  strength  had  risen  to 
0.5  ma.  in  about  three  minutes,  when  the  patient,  who  had 
hardly  perceived  the  current,  began  to  show  symptoms  of 
cocaine  poisoning.  The  application  was  removed  at  once, 
but  he  rapidly  got  worse,  the  heart's  action  became  feeble, 
and  the  patient  prostrate,  the  effect  lasted  for  two  hours. 
It  is  likely  that  the  cocaine  ions  were  transmitted  into  the 
system  not  only  through  the  pulp  but  also  through  the 
lacerated  peridontal  membrane,  but  it  is  not  like  y  that 
more  than  y-g  grain  of  cocaine  was  on  the  application,  of 
which  not  one-half  had  been  formed  into  cocaine  ions.  There 
was  no  likelihood  of  the  drug  being  swallowed,  as  it  was 
easily  controlled  in  that  position  in  the  mouth. 


CHAPTER    IX. 
PHYSIOLOGICAL  EFFECTS  OF  CURRENTS. 

Cataphoric  Effects — Electrolytic  Effects — Path  of  the  Current  in  the 
Body — Motor,  Sensory,  and  Special  Nerve  Effects — Effects  of  the  Current 
on  Nutrition — Effects  of  the  Current  on  Salivary  Glands — Resistance 
Effects  of  Current  Passing  through  the  Body. 

Cataphoric  Effect. — The  phenomenon  of  eataphoresis  is 
dependent  on  the  laws  governing  osmosis  and  the  osmotic 
effect  of  a  continuous  electric  current  on  certain  liquids 
and  compounds  by  which  they  are  conducted  en  masse 
through  a  porous  septum  in  the  direction  of  flow  of  the 
current;  that  is,  from  the  positive  to  the  negative.  It  is 
based  on  the  discoveries  and  experiments  of  many  eminent 
workers  in  electrotherapeutics.  Porret,  in  1815,  explained 
this  tendency  of  fluids  to  be  transported  in  the  direction 
of  flow  of  current,  and  later  the  investigations  of  Becquerel, 
Munk,  Galitien,  Wisse,  W.  J.  Morton,  and  others  have 
added  light  to  the  subject.  Most  modern  works  on  electro- 
therapeutics contain  some  explanation  of  the  cataphoric 
effect  of  the  current,  but  medical  writers,  as  a  rule,  pay 
little  attention  to  it,  and  seem  to  be  sceptical  of  the  reality 
of  cataphoric  effect  when  applied  to  the  body  for  the  osmotic 
medium.  They  seem  to  be  unable  to  separate  it  from  other 
effects  which  take  place  at  the  same  time  when  a  current 
is  passed  through  the  body,  and  far  more  attention  is  being 
given  at  the  present  time  to  other  electrolytic  effects  of 
the  current.  That  this  phenomenon  takes  place  there  can 
be  no  doubt,  but  to  what  extent  it  is  applicable  in  electro- 
therapeutics from  a  dental  aspect  will  be  described  in 
another  part,  at  present  the  theory  of  eataphoresis  will  be 
dealt  with. 


CATAPHORESIS  221 

"Osmotic  pressure1  is  that  force  which  determines  the 
movements  and  the  rate  of  exchange  between  solutions 
in  immediate  contact  or  separated  by  membranes,  more 
or  less  permeable.  Substances  in  solution  move  from  more 
concentrated  regions  toward  regions  less  concentrated,  while 
the  fluid  moves  in  the  opposite  direction.  This  movement 
constitutes  the  phenomenon  of  diffusion,  and  osmotic  pres- 
sure is  the  motive  force  which  animates  matter  in  this  way 
and  produces  diffusion." 

The  rate  of  osmotic  diffusion  is  influenced  by  conditions 
of  temperature,  relative  degree  of  density,  chemical  action, 
and  relative  concentration  of  the  separated  fluids  in  the 
same  circumstances  as  regards  kind  of  separating  medium 
and  quantity  of  fluid  employed  in  the  experiment.  Slightly 
higher  temperature  will  raise  the  osmotic  pressure;  greater 
densities  are  slower  in  osmotic  effect  than  weaker  solutions ; 
fluids  of  acid  reaction  are  more  rapid  than  alkalies.  Osmosis 
of  liquids  of  different  concentrations  follow  the  same  laws 
which  govern  osmosis  of  gases  in  the  spaces  which  contain 
them. 

An  electric  current  passed  through  solutions  separated  by 
porous  membrane,  wTill  greatly  facilitate  osmotic  pressure  in 
the  direction  of  flow  of  current. 

This  fact  may  be  demonstrated  by  the  experiment  of 
placing  two  fluids  of  different  densities  in  a  U-shaped  glass 
tube  which  is  divided  in  the  middle  by  a  porous  membrane 
which  admits  of  ordinary  osmotic  effects.  If  the  two  halves 
contain  the  same  amount  of  fluid,  but  one  side  a  solution 
of  sodium  chloride  and  the  other  pure  water  osmotic  pres- 
sure will  cause  a  tendency  for  the  levelling  up  of  the 
strengths  of  the  solutions  by  the  moving  of  the  weaker 
solution  through  the  membrane  to  the  stronger;  but  if  an 
electric  current  is  passed  through  the  liquid  in  circuit  from 
the  salt  solution  to  the  water  it  will  be  found  that  osmosis 
is  greatly  increased  by  the  action  of  the  current,  and  that 
the  liquid  on  the  positive  side  will  be  forced  through  the 

1  Leduc. 


222 


ELECTRO-THERAPEUTICS 


separating  membrane  into  the  negative  side  increasing  the 
bulk  of  liquid  on  that  side  at  the  expense  of  the  other,  and 
conveying  molecules  of  sodium  chloride  with  it.  This  is 
brought  about  by  electrical  diffusion  or  cataphoric  diffusion, 
and  is  a  simple  illustration  of  the  tendency  of  liquids  to  be 
conveyed  en  masse  in  the  direction  of  flow  of  current.  In 
addition  to  this,  however,  a  formation  of  gases  takes  place 
at  each  electrode,  oxygen  at  the  positive  and  hydrogen  at 
the  negative. 


Fig.  129 


Fig.  130 


+ 


NaCl 
HoO 


NaCl 
Membrane 


U-shaped  tube  before  a  current  is 
passed. 


Effect  of  current  on  solution  in 
tube. 


This  movement  of  the  molecules  of  liquid  in  the  direction 
of  flow  of  current  coincides  to  some  extent  with  Faraday's 
law  of  electrolysis,  which  says  that  electricity  flows  with 
matter   through   it. 

W.  J.  Morton1  has  detailed  a  number  of  physical  experi- 
ments to  prove  the  osmotic  effect  of  the  current,  and 
demonstrated  by  them  that  by  the  action  of  the  current 
fluids  move  en  masse  in  an  electrolyte  from  the  +  to  the 
—  electrode. 

The  author  has  tried  many  of  these  experiments  and  in 


1  Cataphoresis,  p.  91. 


CATAPHORESIS  223 

every  instance  has  obtained  the  result  described,  although 
he  does  not  deduce  the  same  conclusion  from  the  phenomena 
in  every  case. 

Repeating  Dr.  Morton's  experiments  it  will  be  found  that 
if  a  +  electrode  be  placed  in  one  side  of  a  ball  of  moist  clay 
and  a  —  electrode  in  the  opposite  side  and  a  current  passed, 
drops  of  moisture  collect  about  the  —  electrode,  this  is  a 
physical  transfer  of  water  in  the  direction  of  flow  of  current. 

If  a  +  electrode  be  placed  in  a  piece  of  raw  meat  with  a  — 
electrode  some  distance  away  a  similar  transfer  of  moisture 
from  the  tissues  will  take  place  to  the  —  electrode,  and  the 
tissue  will  contract  about  the  +  electrode  and  adhere  to 
it  in  consequence  of  the  coagulation  of  albumen  by  some 
chemical  substance  formed. 

The  author  has  done  similar  experiments  with  coagu- 
lated albumen  using  platinum  electrodes;  drops  of  water 
exude  about  the  —  electrode  and  the  albumen  contracts  and 
adheres  firmly  to  the  +  electrode. 

These  effects  may  be  purely  cataphoric,  but  some  other 
experiments  quoted  by  Dr.  Morton  hardly  come  under  the 
cataphoric  effect;  for  example,  if  two  copper  electrodes  be 
placed  in  coagulated  albumen,  at  the  +  electrode  a  green 
stain  will  be  produced;  at  the  —  electrode  drops  of  water 
but  no  green  coloring.  This  green  stain  should  not  be 
attributed  to  cataphoresis,  it  is  an  ionic  effect  caused  by 
the  dissociation  of  copper  ions  from  the  surface  of  the 
soluble  copper  electrode  which  migrate  in  the  direction 
of  the  —  element;  the  transfer  of  liquid  to  the  site  of  the  — 
electrode  is  brought  about  by  cataphoresis,  so  that  the 
two  phenomena  occur  simultaneously.  Take  a  hard-boiled 
egg  and  cut  it  lengthways  and  remove  the  yolk,  place  the 
white  in  a  saucer  containing  a  solution  of  iodine  and  fill  the 
hollow  of  the  section  of  egg  with  weak  starch  water,  connect 
the  iodine  solution  with  a  negative  electrode  and  the  starch 
with  a  positive  electrode.  On  passing  a  current  the  iodine 
will  pass  through  the  albumen  and  give  the  iodine  test 
with  starch.  This  can  hardly  be  demonstrated  as  a  cata- 
phoretic  effect  because  the  reaction  takes  place  against  the 


224  ELECTRO-THERAPEUTICS 

direction  of  flow  of  current,  but  this  is  one  of  the  experi- 
ments which  W.  J.  Morton  uses  to  amplify  cataphoresis ; 
it  is,  in  fact,  a  good  example  of  the  migration  of  iodine  ions 
from  the  negative  pole.  Quoting  further  from  W.  J.  Morton 
(p.  83),  "Cataphoresis  is  essentially  a  property  of  currents. 
The  fact  that  the  transporting  power  of  the  current 
diminishes  and  finally  ceases,  in  direct  ratio  to  the  diminu- 
tion of  resistance,  indicates  to  me  that  in  liquids  we  have 
to  deal  with  what  I  have  called  a  'movable'  resistance  in 
contradistinction  to  what  in  solids  (metals,  etc.)  might 
be  termed  'stationary'  resistances.  From  this  point  of 
view  a  fluid  is  projected  or  moved  along  in  bulk  simply 
because  it  does  offer  resistance."  This  opinion  would 
seem  to  indicate  that  currents  of  considerable  magnitude 
are  required  for  this  transfer  of  liquids  en  masse  when 
cataphoresis  is   carried   out  in   living  tissue. 

Some  authors  have  pointed  out  that  the  transport  of 
liquids  or  compounds  appears  to  take  place  from  the  nega- 
tive toward  the  positive,  in  which  case  it  is  termed 
anaphoresis,1  to  indicate  the  action  at  the  cathode,  but 
this  phenomenon  coincides  with  the  ionic  effect  and  it  is 
probable  that  in  every  such  instance  in  which  colloid  sub- 
stances are  supposed  to  produce  this  anaphoric  effect,  the 
phenomenon  is  due  to  the  migration  of  ions  and  in  no  way 
a  transfer  of  the  substance  en  masse  as  in  cataphoresis  which 
it  is  said  only  takes  place  in  the  direction  of  flow  of  current. 

In  the  medical  electro-therapeutics  very  little  importance 
appears  to  be  attached  to  the  cataphoretic  effect,  because 
such  large  currents  are  required  for  this  to  be  appreciable, 
the  electrolytic  effect  which  is  produced  by  the  passing  of 
a  galvanic  current  through  the  body  is  regarded  as  pro- 
ductive of  ions  in  most  instances  instead  of  cataphoresis, 
and  while  both  phenomena  undoubtedly  occur  in  some 
instances,  it  is  likely  that  ionic  medication  is  the  principal 
effect  which  is  usually  obtained.  Lewis  Jones2  says:  "A 
movement  of  the  electrolyte  comparable  to  osmosis  takes 

1  Guilleminot,  Electricity  in  Medicine,  p.  212. 

2  Medical  Electricity,  p.  304. 


CATAPHORESIS  225 

place  under  the  influence  of  the  current,  and  generally 
occurs  in  the  direction  of  flow  of  the  current,  namely; 
from  the  positive  to  the  negative  poles;  fluids  can  in  this 
way  be  made  to  pass  through  membranes  or  porous  dia- 
phragms against  the  force  of  gravity.  It  has  been  pro- 
posed to  make  use  of  this  process  for  the  introduction  of 
drugs  into  the  body  through  the  skin,  but  the  migration 
of  the  ions  referred  to  is  a  more  important  factor  in  the 
percutaneous  introduction  of  drugs  by  means  of  electric 
current." 

Cataphoresis  has  been  largely  used  in  practice  by  the 
dental  profession,  in  which  it  is  used  principally  for  pro- 
ducing anesthetic  effects  on  sensitive  dentine,  pulps  of 
teeth,  and  periodontal  membrane  with  cocaine.  In  1888 
Dr.  McGraw,  of  California,  read  a  paper  on  the  anaesthetic 
effect  of  cocaine  involution  with  alcohol  on  sensitive  den- 
tine, this  was  among  the  first  of  the  early  writings  on  the 
dental  aspect  of  the  phenomenon,  and  many  practitioners 
have  since  recorded  the  same  effect  with  the  galvanic 
current. 

W.  J.  Morton  is  probably  the  greatest  exponent  of 
cataphoresis.  In  his  work  on  the  subject  he  attributes  all 
the  effects  of  the  current  on  solution  used  for  medication 
with  a  galvanic  current  to  the  phenomenon,  with  the  ex- 
ception of  the  effect  of  the  product  of  soluble  electrodes 
such  as  copper,  iron,  zinc,  etc.,  which  he  designates  as 
"electric  diffusion,"  this  is  what  is  known  now  as  ions  of 
the  metals  which  are  dissolved  by  the  action  of  the  current, 
of  this  he  points  out  with  accuracy  that  "Another  noticeable 
feature  of  electric  diffusion  of  salts  formed  from  soluble 
electrodes  is  that  a  remarkably  low  current  strength  suffices 
to  set  free  a  large  amount  of  the  metallic  salts."  On  this 
point  depends  largely  the  great  usefulness  of  soluble  elec- 
trodes in  producing  antiseptic  salts  in  the  form  of  ions. 

The  practice  of  anaesthesia  of  sensitive  dentine  by  the 
application  of  cocaine  in  guaiacol  with  the  electric  current 
has  occupied  the  attention  of  a  large  section  of  the  dental 
profession    in    America    and    elsewhere.      This    effect    has 


226  ELECTRO-THERAPEUTICS 

always  been  attributed  to  cataphoresis,  and  with  the  teach- 
ing of  such  an  authority  as  Dr.  W.  J.  Morton  no  one  doubted 
that  this  is  the  real  effect,  but  the  author  has  investigated 
this  subject  and  after  a  number  of  years  of  experience 
with  the  current  has  adopted  the  view  that  the  effect  ob- 
tained when  a  continuous  current  is  used  on  oral  tissue  is 
not  a  cataphoretic  effect,  especially  in  the  use  of  cocaine 
or  any  of  its  derivatives  for  the  obtunding  of  sensitive 
dentine.  A  number  of  experiments  and  also  the  practical 
application  of  the  current,  not  only  for  the  treatment  of 
the  hard  tissues  of  the  teeth,  but  more  especially  for  the 
treatment  of  muco-periodontal  tissue,  in  which,  working 
on  the  cataphoresis  theory,  were  often  negative  in  results, 
forced  on  him  the  conclusion  that  the  current  strength 
which  it  is  possible  to  use  on  the  tissues  of  the  mouth  is 
quite  inadequate  to  produce  the  cataphoric  effect;  that  the 
good  results  obtained  were  from  the  production  of  ions 
with  an  exceedingly  low  current  strength. 

When  working  with  the  expectation  of  obtaining  cata- 
phoric effects,  a  low  current  strength  only  being  possible 
on  such  sensitive  tissues  as  periodontal  membrane  or  dentine, 
mixtures  of  drugs  were  employed,  which  were  not  driven 
into  the  tissues  en  masse  for  the  lack  of  sufficient  current 
strength,  but  the  effect  of  the  current  on  these  mixed  drugs 
was  to  set  free  ions  of  their  component  parts.  Results 
obtained  in  these  circumstances  were,  to  say  the  least, 
unreliable,  but  good  results  were  invariably  obtained  with 
simple  salts  from  which  ions  of  an  antiseptic  nature  were 
readily  formed  by  a  low  current  strength.  An  exhaustive 
test  of  this  methods  has  led  him  to  the  conviction  that 
cataphoresis  as  stated  above  is  never  the  effect,  and  is  in 
this  sense  an  exceedingly  bad  term.  Ionic  medication  is 
always  the  only  effect  which  is  produced  in  the  tissues  of 
the  oral  cavity,  when  an  electric  current  is  used  for  medi- 
cation. 

It  is  quite  conceivable  that  a  substance  like  cocaine 
when  acted  upon  by  water  is  split  up  into  ions  and  in 
this  state  is  readily  introduced  by  the  electric  current  into 


CATAPHORESIS  227 

the  microscopic  organic  tissue  of  dentine.  It  is  quite  an 
easy  matter  to  anaesthetize  the  dentine  and  the  pulp  of  a 
sound  tooth  by  drilling  a  small  hole  through  the  enamel 
just  to  the  dentine,  and  by  applying  ^  gr.  of  codraline,  or 
cocaine  dissolved  in  water  with  a  current  strength  of  1  ma. 
for  five  to  eight  minutes.  The  author  has  frequently 
done  this  to  incisors  to  facilitate  the  operation  of  splinting 
loosened  pyorrhoea  teeth.  The  transfer  of  the  anaesthetic 
in  these  cases  is  undoubtedly  an  ionic  effect,  molecules  of 
water  containing  cocaine  cannot  be  transferred  en  masse 
with  so  small  a  current.  On  the  other  hand,  the  author  has 
shown  by  physical  experiment  that  ions  migrate  immediately 
with  a  current  strength  of  0.5  ma. 

The  ion  is  an  inconceivably  small  particle  when  we  con- 
sider that  it  is  only  a  fraction  of  a  molecule.  It  can  be 
readily  transferred  into  a  conducting  channel  of  microscopic 
dimensions  such  as  the  tubuli  of  dentine  with  comparative 
ease,  and  that  it  doe;  travel  with  the  current  has  already 
been  shown  in  the  chapter  on  ions  (p.  47),  where  it  was 
shown  that  ions  are  the  conveyors  of  electrical  charges, 
that  they  move  with  the  current  and  are  the  means  of 
conducting  it,  not  only  in  the  direction  of  flow  but  in  the 
opposite  direction. 

Electrolytic  Effect. — The  electric  current  passing  through 
the  body  has  the  property  of  decomposing  it  at  the  sites 
of  contact  of  the  conducting  media.  Metallic  electrodes  in 
contact  with  tissues  produce  acid  and  oxygen  at  the  anode 
and  alkali  and  hydrogen  at  the  cathode,  by  the  decomposi- 
tion of  the  salts  and  fluids  of  the  body,  these  are  the  pri- 
mary effects;  a  complex  reaction  also  takes  place  dependent 
on  the  kind  of  metal  employed  and  the  composition  of  the 
tissues.  If  a  non-oxidizable  electrode  like  platinum  is 
used  at  the  anode,  chlorine,  oxygen,  and  acid  are  produced, 
as  the  cathode  potassium  is  liberated  which  unites  chemi- 
cally with  water  in  the  tissue  to  form  caustic  potash  and 
hydrogen  is  set  free.  The  production  of  this  caustic  alkali 
in  its  nascent  condition  causes  destruction  of  the  tissues. 
This  caustic  effect  is  sometimes  produced  in  the  hand  and 


228  ELECTRO-THERAPEUTICS 

other  parts  of  the  body;  if  the  electrode  comes  in  contact 
with  the  skin,  a  small  vesicle  is  formed  and  the  skin  is 
destroyed  at  that  part. 

If  the  electrode  is  of  oxidizable  metal  like  copper  or  zinc, 
the  effect  at  the  anode  is  a  combination  of  the  metallic 
product  with  chlorine  of  the  tissue  and  the  formation  of 
chloride  of  copper  or  chloride  of  zinc;  at  the  cathode  the 
metal  is  not  dissolved,  but  the  caustic  effect  is  produced. 

The  electrolytic  effect  of  the  current  is  utilized  in  medical 
practice  for  producing  coagulation  of  blood  in  aneurysm, 
at  the  anode  a  firm  small  clot  is  formed  and  an  acid  re- 
action produced,  at  the  cathode  a  more  diffused  alkaline 
clot. 

The  complex  structure  of  an  electrolyte  like  the  body  is 
productive  of  numerous  electrolytic  effects  dependent  on 
the  kind  and  position  of  the  electrode,  but  the  acid  and 
oxygen  at  the  anode  and  the  alkali  and  hydrogen  at  the 
cathode  are  constant  effects.  In  practice  the  electrolytic 
effects  on  soluble  electrodes,  notably  zinc  and  copper,  are 
of  inestimable  value  for  their  antiseptic  effects  on  the 
tissues. 

When  a  metallic  electrode  is  placed  in  tissue,  as,  for 
example,  a  thin  copper  probe  in  an  alveolar  fistulous  tract, 
after  the  current  has  passed  for  a  while  the  electrode  will 
adhere  firmly  to  the  tissues  if  the  current  is  of  positive 
sign;  if  the  poles  are  now  reversed  the  tissues  at  once  re- 
lease their  contraction  about  the  electrode  and  it  is  easily 
removed. 

Path  of  the  Current  in  the  Body. — When  a  current  is  passed 
through  any  part  of  the  body,  it  is  not  conducted  from 
one  electrode  to  the  other  in  a  direct  course,  but  branches 
out  in  curves  and  at  right  angles  to  the  points  of  contact, 
the  lines  of  current  are  denser  at  these  points  and  radiate 
from  them  (see  Density,  p.  73).  Lewis  Jones,  in  describing 
diffusion  of  current  in  the  body,  says,  "  The  path  of  a  cur- 
rent between  two  electrodes  placed  upon  the  body  surface 
is  not  to  be  marked  out  simply  by  drawing  direct  lines  from 
one  to  the  other,  for  the  whole  of  the  conducting  tissues 


ELECTROLYTIC  EFFECT  229 

between  the  electrodes  help  to  provide  a  passage  for  the 
current,  which  spreads  out  from  beneath  the  positive 
electrode,  becoming  less  and  less  dense  as  it  occupies  a 
wider  and  wider  sectional  area  of  the  conductor,  and  again 
grows  denser  as  its  lines  of  passage  once  more  gather 
together  to  reach  the  negative  electrode."  According  to 
this  description  of  the  lines  of  current  a  positive  electrode 
applied  to  periodontal  membrane  in  the  incisor  region 
would  show  divergence  of  direction  something  after  the 
lines  of  the  diagram.  With  a  small  spear-shaped  electrode, 
such  as  indicated  on  the  diagram,  the  density  of  current 
is  greatest  at  the  very  end,  and  radiations  of  current  take 

Fig.  131 


■  i — Electrode 


Lines  of  current  diffusion  about  a  positive  electrode  placed  in 
periodontal  tissue. 

place  in  all  directions  from  the  surface  of  the  electrode, 
which  is  brought  in  contact  with  the  moistened  tissues. 
Electrodes  of  such  small  area  and  cross-section,  intensify 
the  density  as  already  stated  (see  p.  74);  for  this  reason 
a  very  small  current  strength  produces  an  effect  on  the 
tissues  equal  to  that  produced  by  a  very  much  greater 
current  strength  applied  with  electrodes  of  large  area,  but, 
of  course,  only  acts  on  a  much  smaller  surface.  A  con- 
tinuous current  passing  into  the  tissues  from  an  electrode 
which  measures  2  sq.  mm.  concentrates  the  flow  of  current 
from  its  surface  to  an  extent  which  makes  it  possible  to 
medicate  or  stimulate  the  tissues  more  perfectly  (in  a 
tissue  of  such  small  resistance  to  current  as  periodontal 


230  ELECTRO-THERAPEUTICS 

tissue)  with  a  current  strength  of  only  2  ma.  than  would 
a  flat  electrode  of  2000  sq.  mm.  (applied  to  the  surface 
of  a  high  resisting  tissue  like  the  skin)  with  a  current 
strength  of  say  20  ma.  So,  also,  if  a  large  flat  electrode 
be  applied  to  the  surface  of  the  gums  the  density  of  the 
current  is  reduced  and  the  penetration  of  medicines  applied 
in  this  maimer  will  be  very  slight  with  a  small  current 
strength. 

The  diffusion  of  current  in  the  body  and  effects  of  density 
are  of  great  practical  value  in  dental  electrical  treatment; 
the  concentration  of  current  from  small  electrodes  permits 
of  perfect  means  of  medicating  diseased  periodontal  tissue 
with  a  current  strength  which  is  readily  tolerated  by 
such  sensitive  tissues,  at  the  same  time  the  electrolytic 
effect  produced  at  the  positive  pole  is  usually  non-pro- 
ductive of  caustic  effects;  the  effect  of  density  is  therefore 
a  great  aid,  rather  than  detrimental  in  this  method  of  using 
the  current. 

Motor,  Sensory,  and  Special  Nerve  Effects. — When  a  con- 
tinuous current  is  passed  through  the  living  body  it  has 
the  effect  of  stimulating  the  motor,  sensory,  or  special 
nerves  nearest  to  the  point  of  contact  of  the  active  electrode. 
When  a  current  is  applied  to  a  motor  nerve  it  causes  con- 
traction of  the  muscle  which  that  nerve  supplies;  in  the  case 
of  a  sensory  nerve  it  conveys  to  the  brain  impressions  of 
sensations  (weak  or  strong)  according  to  the  strength  of  the 
stimulation;  if  the  nerve  trunk  is  an  ordinary  mixed  nerve 
it  conveys  both;  in  the  case  of  nerves  of  special  sense  the 
stimulation  causes  a  response  to  the  particular  sense  which 
the  nerve  ordinarily  controls. 

The  stimulation  of  motor  nerves  occurs  at  the  closure  of 
the  current  if  the  current  be  at  least  about  1  milliampere, 
and  at  both  make  and  break  of  the  circuit  if  the  current  is 
a  strong  one.  This  will  depend  on  the  position  of  the  nerve 
stimulated;  the  superficial  nerves  will  respond  to  a  direct 
stimulation  with  a  very  small  current  strength,  while  a  deep- 
seated  nerve  trunk  will  require  a  larger  current  to  effect 
a  stimulation  and   contraction   of  the  muscle  it  supplies. 


MOTOR  AND  SENSORY  NERVE  EFFECTS  231 

Stimulation  of  motor  nerves  only  occurs  at  make  or  break 
of  current  and  is  a  spasmodic  single  contraction,  which 
does  not  continue  except  the  current  be  a  very  large  one 
even  though  it  continues  to  flow. 

If  the  current  is  a  rapidly  interrupted  one,  as  from  an 
induction  coil,  the  stimuli  to  the  nerve  are  so  rapid  that 
the  contractions  become  tetanic,  there  is  not  time  between 
make  and  break  of  the  current  to  permit  of  relaxation  or 
recontraction,  so  the  muscles  supplied  by  the  stimulated 
nerve  contract  tetanically.  This  effect  of  stimulation  of 
the  nerve  supply  to  certain  muscles  is  much  resorted  to  in 
medical  practice  for  practical  testing  of  certain  muscles 
from  certain  points  called  motor  points,  from  which  muscles 
are  stimulated  to  produce  contraction  effects  for  diagnosis 
of  disease,  its  bearing  has  little  to  do  with  dental  treatment. 

Certain  forms  of- discharges  from  high  frequency  machines 
will  also  produce  motor  stimuli. 

The  stimulation  of  sensory  nerves  is  influenced  to  a  great 
extent  by  the  strength  of  the  current  and  the  density  at 
the  point  of  stimulation;  the  nature  of  the  ions  which  are 
introduced  at  the  point  of  contact  of  electrodes  vary  the 
sensation;  with  some  the  penetration  at  the  cathode  pro- 
duces more  pain  than  at  the  anode,  but  generally  the 
reverse  is  the  case.  The  sensory  stimulation  of  mucous 
tissue  is  productive  of  a  feeling  of  pricking  of  a  vast  number 
of  fine  needles;  on  periodontal  tissue  of  a  burning  sensation. 
These  sensations  are  increased  or  diminished  with  the  area 
and  cross-section  of  the  electrode.  If  a  small  continuous 
current  is  passed  with  a  very  small  electrode  the  sensation 
is  one  of  tingling,  burning  at  the  point  of  contact,  an  im- 
pression which  would  be  wholly  lost  with  a  larger  electrode 
conveying  the  same  amount  of  current.  Interrupted 
currents  produce  sensations  of  shock,  the  severity  of  which 
will  depend  on  the  electro-motive  force;  if  the  interruptions 
are  exceedingly  rapid  the  sensation  produced  is  a  benumbed 
effect,  this  is,  a  true  anaesthetic  effect  which  has  been  utilized 
occasionally  for  the  operation  of  extraction  of  teeth  "with- 
out pain,"  a  principle  which  has  been  much  questioned  in 


232  ELECTRO-THERAPEUTICS 

some  quarters  as  to  its  true  efficiency,  but  which  no  doubt 
is  a  real  anaesthetic  effect,  by  which  sensation  of  pain  is 
benumbed. 

A  continuous  current  of  10  to  12  ma.  passed  with  a 
small  anode  into  the  periodontal  tissues  in  the  molar 
region  of  the  superior  maxilla  will  sometimes  cause  what 
the  patient  describes  as  dizziness,  but  in  fact  is  a  general 
anaesthesia  effect;  how  far  this  can  be  carried  it  is  difficult 
to  say.  The  writer  has  a  patient  on  whom  he  has,  on  sev- 
eral occasions,  noticed  this  general  anaesthetic  effect  when 
a  small  zinc  electrode  is  placed  into  a  pyorrhoea  pocket 
between  the  second  and  third  upper  molars  and  a  current  of 
10  ma.  applied  for  about  five  minutes;  for  the  first  minute 
or  so  slight  tingling  pain  is  the  effect  of  the  stimulus,  but 
soon  the  parts  become  numb  and  when  the  current  is  raised 
to  10  ma.  for  a  short  time,  the  patient  behaves  as  if  passing 
under  the  effects  of  a  general  anaesthetic,  but  is  easily  roused 
on  removal  of  the  current,  and  described  the  feeling  as  that 
of  dizziness;  the  senses  of  hearing  and  sight  are  also  dulled, 
but  respiration  is  not  affected. 

The  stimulation  of  nerves  of  special  sense  gives  rise  to 
effects  peculiar  to  the  sense  which  is  dependent  on  the 
particular  nerve.  Stimulation  of  the  olfactory  nerve  gives 
rise  to  a  sense  of  smell,  the  auditory  nerve  to  the  intensi- 
fying of  sound,  the  optic  nerve  gives  rise  to  sensation  of 
flashes  of  light.  The  stimulation  of  the  optic  nerve  through 
the  filaments  of  nerves  connecting  it  with  the  nerves  of  the 
teeth  is  the  best  example  of  stimulation  of  nerves  of  special 
sense.  A  continuous  current  applied  to  any  of  the  teeth  in 
either  the  maxilla  or  mandible,  with  a  current  strength  of 
1  ma.  or  more  passing  through  dentine  or  cementum  of 
live  teeth,  at  make  and  at  break  of  current,  the  stimulus 
will  cause  a  flash  of  light  in  the  eye  which  receives  the 
stimulus;  this  flash  is  very  vivid  and  resembles  lightning. 
It  has  long  been  known  that  current  applied  to  the  vicinity 
of  the  eye,  as  on  the  closed  eyelid,  causes  stimulation  of 
the  retina,  which  produces  effects  of  different  colored  lights, 
some  say  dependent  on  the  pole  which  is   used.     With 


SPECIAL  NERVE  EFFECTS  233 

stimulation  through  the  dental  nerves  the  flash  is  always 
a  bright  white  light,  and  is  produced  by  either  anode  or 
cathode  at  the  make  or  break  of  circuit. 

Stimulation  of  nerves  of  taste  produces  a  metallic  taste. 
This  is  noticed  by  patients  taking  galvanic  baths  when 
the  bath  comes  above  the  shoulders. 

Effects  of  Current  on  Nutrition. — Experiments  on  animals 
have  shown  that  treatment  with  constantly  varying  cur- 
rents have  the  effect  of  increasing  their  weight;  a  com- 
parative test  in  which  some  young  dogs  of  one  litter  were 
treated  and  others  not,  all  being  fed  and  kept  under  iden- 
tically the  same  conditions,  those  which  were  treated  by 
general  faradization  improved  in  physical  condition  and 
gained  tissue  weight  over  those  which  were  not  treated. 
Similar  experiments  have  been  carried  out  with  chickens 
in  which  it  has  been  found  that  they  improve  in  size  and 
weight  at  a  rapid  rate,  owing  to  stimulation  by  current. 
Rhythmical,  interrupted,  and  sinusoidal  currents  are  said 
to  have  the  best  effect  on  general  nutrition,  while  con- 
tinuous currents  or  static  electricity  to  be  less  effective. 
The  benefits  derived  from  general  electrical  treatment  are 
recognized  by  the  medical  profession,  and  many  forms  of 
treatment  are  employed  for  general  stimulation  of  the 
body  to  secure 'improvement  in  certain  morbid  conditions. 

Effects  of  Current  on  Salivary  Glands. — Continuous  cur- 
rents of  small  strength  applied  in  the  vicinity  of  nerve 
supply  to  salivary  glands  cause  increased  secretion  by 
stimulating  the  nerves  controlling  the  blood  supply  and 
increasing  functional  activity  of  the  glands;  copious  supply 
of  saliva  will  be  excited  in  the  sublingual  glands  by  applying 
an  electrode  to  the  soft  tissue  in  the  region  of  the  lower 
incisors,  cuspids,  and  biscupids;  the  submaxillary  glands 
are  excited  by  application  of  current  to  the  region  of  the 
lower  molars,  and  the  parotid  glands  are  excited  by  applica- 
tion to  the  bicuspid  or  molar  region  of  the  superior  maxilla. 
Generally  speaking,  electric  stimulus  to  the  nerve  supply 
of  secreting  glands  of  the  body  increases  secretory  activity 
of  the  cells  and  causes  an  increase  of  their  secretions. 


234  ELECTRO-THERAPEUTICS 

Resistance  Effects  of  Current  Passing  through  the  Body. — 
The  resistance  of  the  body  is  a  very  complex  problem; 
unlike  a  metallic  conductor,  the  tissues  vary  in  conductivity 
according  to  the  kind  to  which  electrodes  are  applied,  and 
even  in  the  same  kind  it  varies  from  day  to  day.  The  skin 
offers  the  most  resistance  to  the  passing  of  current,  and  this 
varies  according  to  whether  it  be  moist  or  comparatively 
dry  (perfectly  dry  skin  is  a  bad  conductor). 

Nerve,  blood,  and  muscle  are  in  that  order  the  best  con- 
ductors of  current.  Guilleminot  says:  "The  blood  plays 
an  important  role  in  the  conductivity  of  the  body.  Like 
the  other  fluids  of  the  body,  it  is  composed  of  a  solution  of 
salts,  acids,  and  bases,  and  of  non-electrolytes,  albumins, 
sugars,  and  fats." 

If  electrodes  be  placed  in  a  mucous  tissue  the  resistance 
is  much  less  than  if  the  epidermis  is  the  site  of  contact. 
This  has  been  explained  by  Leduc  by  the  idea  of  migration 
of  ions,  the  skin  being  poor  in  ions,  the  interchange  of  ions 
from  the  skin  to  the  electrode  or  from  the  electrode  to  the 
skin  is  imperfect  and  resistance  to  passing  of  current  is 
raised;  but  if  the  parts  are  saturated  with  a  saline  solution 
which  is  rich  in  ions,  the  contact  becomes  more  complete  by 
the  passing  of  ions  and  resistance  is  reduced.  If  the  anode 
is  applied  to  periodontal  membrane  with  the  hand  as  con- 
tact for  the  negative  element,  the  resistance  of  the  body  is 
often  found  to  become  less  as  the  application  goes  on  up 
to  a  point,  especially  if  the  hand  electrode  is  kept  well 
moistened  or  if  a  carbon  electrode  placed  in  saline  solution 
is  used  and  the  whole  hand  immersed  in  the  solution. 

Different  methods  have  been  devised  for  measuring  the 
resistance  of  the  body  such  as  the  Wheatstone's  Bridge, 
Mergier's  ohm  meter,  etc.  These  are  generally  constructed 
on  the  principle  of  a  known  E.  M.  F.  and  current  strength 
from  which  may  be  calculated  the  resistance  according  to 
Ohm's  law,  but  for  all  practical  purposes,  if  it  is  required 
to  ascertain  the  resistance  of  a  patient  in  circuit,  it  is  easy 
to  calculate  it  according  to  Ohm's  law  if  the  electro-motive 
force  at  the  electrodes  on  the  patient's  body  is  known  and 


RESISTANCE  OF   THE  BODY  235 

the  milliampere  meter  indicates  the  current  strength  which 
is  passing. 

Say,  for  instance,  a  battery  or  current  switchboard  which 
is  equipped  with  a  reliable  voltmeter  showing  the  E.  M.  F. 
in  volts,  indicates  that  4  volts  is  producing  a  current 
strength  of  2  milliamperes  in  treating  a  patient  in  circuit 
the  resistance  of  the  patient  is  calculated 

E   =  R        4  volts  =  2000  ohms. 

C  0.002  ampere 

The  distance  the  electrodes  are  placed  apart  also  affects  the 
resistance.  Some  operators  on  treating  periodontal  mem- 
brane have  advocated  the  placing  of  the  negative  electrode 
near  the  site  of  ionization,  on  the  neck  or  under  the  chin, 
in  which  case  the  resistance  will  be  found  to  be  much  less 
than  if  the  electrode  is  as  far  away  as  the  hand. 

But  the  measurement  of  resistance  is  not  an  essential 
factor  in  the  use  of  the  current  therapeutically,  except  in 
respect  to  amount  of  discomfort  which  might  be  caused. 
It  is,  however,  an  interesting  point  in  the  constant  use  of 
the  current  to  note  the  variation  of  resistance  in  different 
patients  and  in  the  same  patient  at  different  times. 

Observations  of  the  author  led  him  to  conclude  that 
temperament  or  disposition  of  a  patient  has  an  effect  on 
the  resistance  of  the  body;  calm,  phlegmatic,  non-excitable 
people  appear  to  conduct  current  better  than  the  nervous, 
excitable,  or  irritable.  The  general  health  of  the  body 
appears  also  to  have  an  influence  on  resistance;  those  in 
perfect  health  appear  to  be  better  conductors  of  current, 
and  resistance  is  increased  in  those  suffering  from  toxic 
effect  of  oral  sepsis.  The  resistance  of  the  body  from  the 
mouth  to  the  hand  varies  considerably  and  is  dependent 
on  a  number  of  conditions,  but  generally  under  conditions 
which  may  be  considered  almost  identical,  measuring  it 
when  an  active  electrode  of  small  diameter  is  placed  in  the 
mucoperiodontal  tissue  and  the  indifferent  electrode  is 
moistened  and  held  in  the  hand,  the  range  may  be  any- 
thing between   1300  and  3500  ohms.     Resistance  is  very 


236  ELECTRO-THERAPEUTICS 

much  increased  if  tooth  structure  is  included,  i.  e.,  the 
active  electrode  placed  in  contact  with  the  dentine  and  the 
indifferent  electrode  held  in  the  hand,  and  it  is  further 
increased  if  the  tooth  is  dead ;  the  enamel  of  tooth  structure 
resists  the  passing  of  current  completely  if  no  moisture  is 
present  to  conduct  over  its  surface. 

The  measurement  of  resistance  of  dentine  through  the 
body  is  dependent  on  such  a  number  of  circumstances 
that  it  is  almost  impossible  to  formulate  any  accurate  law 
which  may  be  said  to  govern  all  cases.  Opinions  vary  so 
widely  on  this  point  that,  it  is  well  that  accuracy  in  this 
particular  has  little  bearing  on  the  therapeutic  effects  of 
the  current  in  its  uses  for  dental  purposes.  Allowances 
must  be  made,  in  measuring  resistance,  for  variety  in  density 
of  the  tissue,  distance  between  the  poles,  condition  of  the 
skin  at  contact  of  the  indifferent  electrode,  conductivity 
of  the  body  in  different  individuals,  in  health,  or  in  certain 
diseases. 

Professor  G.  Weiss1  places  resistance  of  the  body  from 
hand  to  hand,  in  the  cases  of  16  men  measured,  at  an 
average  of  1300  ohms,  and  in  7  women  at  1500  ohms. 

Dawson  Turner2  gives  resistance  from  hand  to  hand  at 
1375  ohms. 

Lewis  Jones3  gives  resistance  as  ranging  between  1000 
ohms  and  2000  ohms  "under  conditions  of  medical  practice 
and  using  salt  water  to  moisten  the  skin." 

The  average  of  150  cases  recorded  by  the  writer  from 
the  periodontal  tissue  of  the  mouth  to  the  hand  holding  a 
moistened  electrode  was  3250  ohms,  but  it  must  be  noted 
that  here  the  one  electrode  tried  was  of  a  very  small 
area. 

This  estimate  was  arrived  at  by  recording  the  E.  M.  F. 
from  the  reading  of  a  volt-meter  attached  to  the  terminal 
of  a  main  current  switchboard,  and  the  current  strength 
indicated  by  milliampere  meter,  the  patient  being  in  circuit 

1  Arch.  d'Electricite  Medicale,  1893. 

2  Practical  Medical  Electricity,  p.  188. 

3  Medical  Electricity,  p.  302. 


RESISTANCE  OF   THE  BODY  237 

holding  a  metallic  electrode  covered  with  moistened  lint. 
The  average  was  13  volts  and  4  ma. 

13  volts 

R  =  rTT^ T~    =  3250  ohms. 

0.004  ampere 

Similar  measurements  through  dentine  from  tooth  to  hand 
gave  a  varied  resistance  corresponding  with  the  thickness 
of  the  dentine  and  whether  the  teeth  were  alive  or  dead; 
one  record  from  the  surface  of  an  erosion  at  the  neck  of  a 
live  tooth  was  5000  ohms,  another  from  a  slight  approximal 
cavity  in  a  superior  central  incisor  was  7500  ohms;  a  dead 
superior  premolar  with  open  apical  foramen  was  4000 
ohms.  The  highest  recorded  estimate  of  resistance  in  live 
dentine  was  10,000  ohms,  and  this  might  be  due  to  the  very 
small  area  of  the  dentine  and  size  of  the  electrode.  It  is 
evident  that  resistance  of  dentine  is  a  variable  quantity, 
and  it  is  difficult  to  give  a  definite  estimate  of  what  it  is 
as  a  rule.  Some  authors  have  placed  it  very  much  higher 
than  these  estimates  here  given. 

Dr.  Louis  Jack1  states  that  "resistance  of  the  body 
including  the  dental  tissues  varies  from  10,000  to  70,000 
ohms,"  and  the  same  writer,  in  quoting  Dr.  W.  A.  Price, 
states  that  author's  estimate  of  resistance  "from  cavity 
to  the  hand"  is  about  25,000  ohms.  It  is  not  stated  how 
these  measurements  were  obtained,  but  if  the  estimates 
of  other  eminent  medical  electro-therapeutic  authors 
quoted  are  correct  in  their  calculation  of  resistance  of 
the  body  from  one  distant  part  to  another,  e.  g.,  from 
hand  to  hand  (taken,  for  example,  the  highest  given  that 
of  2000  ohms),  there  is  a  difference  of  8000  to  68,000  in 
these  greatest  estimates  to  be  attributed  to  resistance  of 
dentine.  In  the  latter  case  no  ordinary  18-cell  battery 
producing  E.  M.  F.  of  24  volts  could  furnish  sufficient 
current  to  overcome  so  great  a  resistance,  consequently 
no  current  would  pass.    According  to  Ohm's  law, 

24  volts 

R  =  7^ T-    =  48,000  ohms. 

.0005  ampere 

1  Kirk's  Text-book  of  Operative  Dentistry,  p.  160. 


238  ELECTRO-THERAPEUTICS 

that  is,  if  24  volts  are  required  to  pass  a  current  of  0.5  ma. 
through  the  dentine  of  a  tooth,  the  resistance  would  be 
48,000  ohms,  which  is  considerably  under  the  estimate  of 
70,000  ohms. 

The  writer  has  not  found  it  necessary  to  use  more  than 
20  volts  to  pass  a  current  of  2  ma.  through  the  dentine 
of  a  live  tooth  from  a  small  drill  hole  just  through  the 
enamel,  with  the  body  included  in  circuit  to  the  hand. 
It  is  due  to  the  density  of  the  current  in  a  small  area  that 
conduction  by  ions  overcomes  resistance.  If  this  calcula- 
tion is  correct,  the  resistance  from  tooth  to  hand  through 
dentine  in  the  case  of  20  volts  with  known  amperage  of 
2  ma.  is 

20  volts 

R  =  — =  10.000  ohms. 

2  ma. 

In  dead  teeth  the  resistance  offered  to  current  will  depend 
somewhat  on  whether  the  canal  is  open  at  the  apex  and 
if  there  is  organic  matter  or  liquid  contained  to  act  as  a 
conductor  of  current.  If  the  apex  is  sealed  with  a  non- 
conductor like  gutta-percha  the  resistance  will  be  much 
increased,  as  conduction  will  then  have  to  be  through  the 
dentine  and  cementum,  but  with  an  open  apical  foramen 
and  a  liquid  solution  contained  in  the  canal  into  which  an 
electrode  can  be  passed,  conduction  of  current  by  this 
channel  is  comparatively  easy,  and  resistance  is  not  as  great 
as  it  is  in  the  case  of  a  layer  of  dentine. 


CHAPTER  X. 
ELECTRO-THERAPEUTIC  EFFECTS. 

Ionic  Medication — From  a  Dental  Aspect — The  Zinc  Ion — The  Silver 
Ion — The  Cocaine  Ion — The  Adrenalin  Ion — The  Salicylic  Ion — Advan- 
tages of  Ionic  Medication — Effects  of  Ions  on  Bacteria. 

The  Therapeutic  Effects  of  electrical  currents  have 
engaged  the  attention  of  the  medical  profession  to  a  great 
extent,  especially  of  late.  The  use  of  the  current  is  not 
confined  to  local  treatment  only,  but  general  treatment  of 
the  whole  body  for  all  kinds  of  morbid  conditions;  static 
and  high-frequency  currents  are  now  considered  of  great 
importance.  Stimulating,  sedative,  and  ionic  are  among 
the  medical  therapeutic  effects  of  different  currents.  In 
surgery  the  continuous  current  is  largely  used  for  cautery, 
light,  and  electrolytic  effects. 

In  Dentistry  the  subject  of  electro-therapeutics  appears 
to  have  been  sadly  neglected;  it  has  met  with  a  certain 
amount  of  support  in  America,  where  the  cataphoric  effects 
have  been  used  for  anaesthesia  and,  to  a  small  extent,  for 
sterilizing  septic  pulp  canals,  but  the  subject  does  not 
seem  to  have  been  seriously  studied.  The  profession  owes 
a  debt  of  gratitude  to  that  great  enthusiast  and  scientist 
W.  J.  Morton,  of  New  York,  for  his  treachings  and  sug- 
gestions of  the  application  of  electricity  to  dental  science. 
In  his  book  C diaphoresis,  Dr.  Morton  made  the  valuable 
suggestion  that  tubuli  of  dentine  can  be  penetrated  by 
drugs  applied  with  the  electric  current,  and  in  the  case  of 
septic  root  canals  the  driving  of  antiseptic  drugs  into  the 
structure  of  the  tooth  and  the  sterilizing  of  the  same  by 
cataphoric  methods  is  far  more  scientific  and  effective  than 
the  ordinary  method  of  placing  antiseptics  in  the  canals. 


240  ELECTRO-THERAPEUTICS 

He  asserts  that  "if  cataphoresis  is  employed  as  a  diffusing 
agent  success  will  be  more  swift  and  sure.  There  is,  in 
addition  to  all  this,  the  possibility  of  carrying  medicaments 
into  the  periodontal  membranes  for  the  treatment  of  acute 
infectious  inflammatory  conditions  of  that  tissue."1  These 
valuable  suggestions  have  not  been  acted  upon  by  the  vast 
majority  of  practitioners  because,  in  the  first  place  technique 
has  been  lacking,  and,  secondly,  the  subject  of  electricity 
has  not  been  studied  at  all,  or  so  superficially  that  success 
in  application  of  the  current  has  been  almost  an  impossi- 
bility. 

In  the  light  of  the  present-day  knowledge  of  electro- 
therapeutics, the  theory  of  cataphoresis  in  dental  applica- 
tion must  give  way  to  ionic  medication,  and  then  the 
greatest  stumbling-block  to  the  success  of  electrical  treat- 
ment of  the  teeth  and  other  oral  structures  will  be  removed. 
By  the  lessons  taught  by  research  of  Leduc,  Lewis  Jones, 
D'Arsonval,  Turner,  and  others,  a  more  comprehensive 
view  of  the  effects,  of  the  different  currents  on  the  body  is 
placed  at  our  disposal.  The  electrolytic  effects  on  certain 
salts  of  an  antiseptic  nature  whereby  ions  are  transported 
into  the  tissues  (and  this  with  a  very  low  current  strength) 
opens  up  a  field  of  usefulness  to  the  dental  profession  of 
inestimable  value.  The  natural  susceptibility  of  the  oral 
cavity  to  septic  infection  constitutes  three-fourths  of  the 
greatest  difficulties  placed  in  the  way  of  almost  every 
operation  the  dentist  is  called  upon  to  perform,  the  burning 
question  ever  being  how  to  prevent  or  to  cure  sepsis.  If, 
then,  an  improvement  on  the  ordinary  method  is  placed  at 
our  disposal  by  the  use  of  electric  currents,  it  should  be  our 
duty  to  adopt  it. 

Ionic  Medication.  —  The  theory  of  the  formation  and 
migration  of  ions  and  the  physiological  effect  of  ions  have 
been  detailed  in  other  parts  of  this  work,  the  therapeutic 
considerations  bring  us  to  the  more  practical  aspect  of 
this  electrolytic  phenomenon.      Certain  principles  peculiar 

1  W.  J.  Morton,  Cataphoresis,  p.  238. 


IONIC  MEDICATION  241 

to  the  formation  and  movement  of  ions  in  the  tissues  must 
not  be  lost  sight  of  in  order  to  get  the  best  results  from  this 
method  of  treatment;  all  substances  are  not  dissociated 
by  the  effect  of  the  current;  ether,  alcohol,  chloroform,  and 
oils  are  some  of  these;  it  therefore  would  be  useless  to 
attempt  ionization  with  these ;  the  dissociation  is  effected  by 
the  solution  and  only  substances  which  form  ions  in  solution 
can  be  "ionized":  water  is  the  only  solvent  which  gives 
any  amount  of  ions,  though  a  few  are  formed  in  some  other 
liquids.  Then,  again,  it  is  necessary  to  know  which  ions  are 
electro-positive  and  which  electro-negative,  that  is,  which 
are  driven  into  the  tissues  from  the  anode  and  which  from 
the  cathode.  Reference  has  been  made  to  this  effect 
already,  and  it  is  not  hard  to  remember  that  metals,  alka- 
lies, hydroxyl,  and  alkaloids  are  repelled  from  the  positive 
pole;  and  acid  radicles,  iodine,  bromine,  etc.,  are  repelled 
from  the  negative  pole;  the  caustic  effect  of  the  negative 
pole  (cathode)  should  not  be  forgotten,  if  by  mistake  the 
negative  non-oxidizable  metallic  electrode  be  applied  to 
the  tissues  of  the  mouth  with  sufficient  current,  formation 
of  caustic  potash  or,  more  important  still,  the  formation  of 
hydrogen  in  the  tissues  might  cause  destruction  of  a  tissue 
which  it  is  desired  to  stimulate  or  treat  with  ions. 

Again,  the  action  of  the  current  on  some  drugs  which 
are  escharotic  or  have  a  caustic  effect  on  tissues  without  a 
current,  are  completely  changed  when  converted  into  ions. 
Iodine  and  chlorine  are  examples  of  this,  as  are  also  some 
strong  acids. 

The  local  effect  of  ionic  medication  is  dependent  on  the 
ion  used.  Nothing  but  experience  can  teach  us  the  effect 
of  the  different  ions,  the  subject  is  comparatively  new; 
nevertheless,  there  is  now  a  vast  amount  of  literature  de- 
tailing the  action  of  ions  of  different  kinds,  and  it  is  most 
noteworthy  that  medical  experience  goes  to  show  that 
treatment  of  mucous  tissues  with  ions  gives  the  surest 
results;  this  is  of  course  not  to  be  wondered  at,  as  it  is  readily 
perceived  that  the  conduction  of  electrically  charged  atoms 

or  groups  of  atoms  must  be  facilitated  by  a  soft,  moist, 
16 


242  ELECTRO-THERAPEUTICS 

good  conducting  electrolyte  such  as  mucous  or  periodontal 
tissue ;  whereas  the  skin,  being  a  poor  conductor,  sometimes 
poor  in  ions  itself,  as  pointed  out  by  Leduc,  penetration  of 
ions  from  medicine  applied  to  it  is  not  so  rapid  and  not 
so  sure. 

To  gather  from  the  experience  of  the  medical  profession 
we  will  do  well  to  examine  the  reports  from  one  of  the 
very  latest  sources.  From  this  many  useful  hints  may  be 
obtained,  which  may  lead  to  more  extensive  use  of  ions  in 
dentistry.  At  a  meeting  of  the  British  Medical  Association 
held  in  Liverpool  in  July,  1912,  Dr.  Lewis  Jones1  read  a 
paper  in  which  he  tabulates  his  own  experience  and  that 
of  the  profession  in  general,  with  zinc,  salicylic,  chlorine, 
iodine,  and  radium  ions;  he  referred  to  reports  made  in 
the  medical  journals  of  Great  Britian  and  on  the  Continent, 
of  successful  treatment  of  a  great  number  of  cases  of  local 
affections.  Lender  the  heading  of  the  zinc  ion  successes 
have  been  reported  in  treatment  of: 

Simple  chronic  ulceration  of  the  leg. 

Bed-sore  ulcerations. 

Rectal  ulcerations. 

Anal  fissure. 

Ulceration  of  the  mouth. 

Pyorrhoea  alveolaris. 

Ulceration  of  the  nose. 

Sinuses. 

Gynecological  conditions. 

Sycosis,  furuncle,  acne. 

Lupus. 

Rodent  ulcer,  etc. 
Numerous  cases  are  recorded  of  all  these  conditions  by  the 
local  application  of  zinc  ions.  Dr.  Lewis  Jones  chronicles 
three  cases  of  chronic  sores  of  the  nasal  cavities  cured 
quickly  under  zinc  ions.  He  says:  "Two  of  these  simulated 
lupus,  but  were  probably  staphylococcal  rather  than  tuber- 
culous.    The  third  was  an  ulcer  just  within  the  nose  in  a 

1  British  Medical  Journal,  August  31,  1912. 


IONIC  MEDICATION  243 

middle-aged  lady;  it  had  persisted  for  several  months,  and 
healed  at  once  after  a  single  treatment."  He  recalls  the 
report  of  a  fistula  in  the  lower  jaw  as  follows:  "Marquis 
and  Pappon1  have  reported  three  successful  cases  of  fistula 
in  connection  with  the  lower  jaw.  The  applications  were 
of  20  milliamperes  of  one  hour's  duration,  and  were  re- 
peated every  seven  days.  From  four  to  six  applications 
were  made,  and  in  each  case  the  zinc  ionization  brought  to 
a  close  a  troublesome  condition  which  had  lasted  for  two 
years  or  more." 

These  are  but  a  few  of  the  very  large  number  of  cases 
reported  of  the  healing  effect  of  zinc  ions. 

Under  the  heading  of  "The  Salicylic  Ion"  he  has  col- 
lected a  number  of  reports  of  cases  of: 

1.  Perineuritis  and  neuralgia. 

2.  Painful  affections  of  muscular  and  fibrous  tissues. 

3.  Arthritis. 

In  addition  to  his  own  vast  experience  in  the  use  of 
this  ion  for  the  successful  treatment  of  this  painful  class 
of  disorders,  refers  to  the  reports  made  by  such  authorities 
as  Leduc,  Desplates,  Verney,  Norin,  Circca  Salse  and 
Dawson  Turner. 

The  chlorine  ion  is  advocated  for  the  softening  of  fibrous 
and  cicatricial  tissue.  From  a  medical  aspect,  the  tabu- 
lating of  these  reports  of  successful  treatment  with  the 
different  ions  at  present  in  practical  use  is  of  great  value. 

From  a  Dental  Aspect. — Very  little  has  been  recorded, 
so  far,  of  the  treatment  of  dental  diseases  by  ions.  Probably 
the  first  mention  in  this  country  is  that  by  the  author  (in 
discussing  a  paper  on  vaccine  therapy  by  Dr.  Ayre  and 
Mr.  Lewis  Payne  before  the  Royal  Society  of  Medicine)2 
in  which  he  said:  "For  a  long  time  by  a  method  of  ionic 
medication  of  the  periodontal  membrane  by  electric  cur- 
rent, he  believed  he  had  been  producing  very  similar  results 
in  the  system  to  those  claimed  by  the  advocates  of  vaccine 

1  Arch,  d'elect.  med.,  1910,  p.  568. 

2 Proceedings  of  the  Royal  Society  of  Medicine  (Odontological  Section), 
vol.  iii,  p.  63. 


244  ELECTRO-THERAPEUTICS 

treatment.  Ions  of  antiseptic  salts  were  driven  into  the 
very  protoplasm  of  the  affected  tissues  and  killed  the 
organisms  in  the  tissues,  and  he  took  it  that  the  dead  organ- 
isms were  absorbed  into  the  blood  stream  and  had  an 
effect  upon  the  opsonins  similar  to  that  of  vaccine  prepared 
from  cultures." 

Later  in  a  paper  read  before  the  Royal  Society  of  Medi- 
cine (Odontological  Section),  1912,  p.  104,  the  writer  made 
the  following  statement:  "It  has  been  conclusively  shown 
by  many  workers  in  electro-therapeutics  that  ions  of  zinc, 
copper,  silver,  and  iodine  have  strong  antiseptic  properties; 
the  principal  advantage  they  possess  over  ordinary  methods 
of  applying  them  in  treatment  is  that  with  their  electrical 
charges  passing  through  an  electrolyte  like  the  body  the 
ions  penetrate  the  cells  of  the  tissues  and  (probably  on 
account  of  a  certain  amount  of  coagulation  of  albumin) 
are  not  readily  affected  by  absorption  into  the  general 
circulation  in  the  same  way  as  drugs  which  are  hypodermic- 
ally  injected;  the  only  question  is  the  depth  to  which  pene- 
tration takes  place;  this  seems  to  me  to  depend  on  the 
amount  of  current  strength  which  is  possible  and  the  kind 
of  tissue  which  is  under  treatment;  periodontal  membrane, 
for  example,  will  permit  of  greater  penetration  than  the 
epidermis. 

In  medical  electro-therapeutics  ions  of  zinc  are  successfully 
used  in  the  treatment  of  such  affections  as  rodent  ulcer, 
lupus,  pus-yielding  sinuses,  etc.  In  dental  practice  there 
are  many  difficult  problems  yet  unsolved;  the  most  difficult 
of  these  is  the  one  in  which  ionization,  to  my  mind,  is  a 
step  in  advance  of  the  other  methods  placed  at  our  dis- 
posal." 

The  application  of  a  number  of  different  ions  used  in  the 
treatment  of  several  dental  disorders  was  also  recorded  at 
that  time. 

For  a  number  of  years  the  writer  used  the  continuous 
electric  current  for  the  treatment  of  pyorrhoea  alveolaris, 
with  the  idea  that  cataphoresis  was  the  effect  obtained, 
the  principle  of  mixing  drugs  of  an  antiseptic  nature  with 


IONIC  MEDICATION  245 

the  expectation  of  driving  them  into  the  affected  tissues 
en  masse  has  since  proved  itself  to  him  to  be  erroneous,  a 
certain  amount  of  success  was  undoubtedly  recorded,  but 
failure  was  frequent,  and  in  the  light  of  present  knowledge 
of  the  electrolytic  effect  where  a  current  is  passed,  the 
writer  is  convinced  that  the  good  effects  obtained,  resulted 
from  the  migration  of  ions  when  solutions  were  used  from 
which  ions  were  readily  obtained,  and  failure  was  the 
result  of  either  neutralization  of  ionic  effect  by  chemical 
reunion  of  ions  of  different  kinds,  thereby  destroying  their 
therapeutic  effect  (which  is  a  doubtful  hypothesis)  or  the 
migration  of  useless  ions. 

In  ionic  medication  it  is  advisable  to  dissociate  a  par- 
ticular ion  and  depend  on  the  therapeutic  value  of  that 
ion  for  the  effect  that  is  desired.  For  instance,  if  the  zinc 
ion  is  required,  a  zinc  electrode  with  a  3  per  cent,  solu- 
tion of  zinc  chloride  with  a  current  strength  of  2  or  3 
milliamperes,  the  zinc  ion  will  dissociate  from  the  chlorine 
ion  at  the  anode,  the  former  migrating  into  the  tissues. 
So,  also,  if  a  copper  ion  is  desired,  a  copper  electrode  and 
a  2  per  cent,  solution  of  sulphate  of  copper  will  furnish 
the  ion  at  the  anode.  But  if  these  solutions  of  salts  are 
incorporated  with  non-conducting  and  non-dissociating  solu- 
tions like  alcohol  or  glycerine  with  the  expectation  of  pass- 
ing them  into  the  tissues  en  masse  by  cataphoric  methods, 
the  current  strength  necessary  for  this  will  exceed  the 
toleration  by  the  patient. 

The  therapeutic  effects  of  ions  on  the  oral  tissue  are  to 
my  mind  of  such  importance  that  it  should  take  the  place 
of  the  present  method  of  treatment  of  nearly  every  form  of 
septic  infection  of  the  periodontal  membrane.  This  effect 
is,  in  the  case  of  ionization  with  an  antiseptic  ion,  that  of 
producing  asepsis  in  a  septic  area  by  the  penetration  of 
the  ions  into  the  tissue  and  the  destruction  there  of  micro- 
organisms which  have  been  absorbed  by  the  tissues.  A 
great  variety  of  different  species  of  bacteria  is  found,  not 
only  in  the  pockets,  but  in  the  tissues  forming  the  boundaries 
of  the  pyorrhoea  pockets,  their  action  on  the  tissue  is  to 


246  ELECTRO-THERAPEUTICS 

destroy  it,  the  pus  being  the  product  of  inflammation 
caused  by  the  presence  of  bacteria.  The  destruction  of 
the  organisms  is  the  main  object  of  all  who  treat  alveolar 
suppuration.  This  is  effectively  done  by  passing  an  electrode 
into  the  affected  pockets  and  by  the  electrolytic  effect  of 
the  current  driving  ions  of  some  antiseptic  salt  into  the 
tissues.  The  depth  of  penetration  of  these  ions  will  depend 
on  the  current  strength  which  is  available.  The  ions  are 
deposited  in  the  tissues,  they  penetrate  the  protoplasm  of 
the  cells  and  radiate  in  all  directions.  The  effect  is  a  local 
sterilization  of  an  area  of  infection  which  cannot  be  reached 
in  any  other  way.  The  practice  of  syringing,  irrigating, 
and  wiping  out  infected  areas  of  tissue  with  antiseptics, 
with  the  hope  of  sterilizing  it,  is  so  inadequate  and  ineffec- 
tive that  the  object  is  defeated  and  little  or  no  permanent 
good  results  are  obtained;  this  is  doubtless  the  experience 
of  that  section  of  the  dental  profession  which  asserts  that 
it  is  useless  to  treat  pyorrhoea  alveolaris  when  pus  persists, 
after  a  trial  of  such  superficial  treatment,  and  asserts  that 
extraction  should  be  advised  There  are  even  those  who 
advise  the  extraction  of  all  teeth  which  are  affected  with 
pus-yielding  pyorrhoea  pockets.  Mr.  J.  F.  Colyer1  says,  "In 
cases  where  there  is  considerable  bone  destruction,  or  where 
in  spite  of  local  treatment,  the  formation  of  pus  persists, 
extraction  of  the  teeth  must  be  resorted  to." 

The  writer  has  proved  to  his  entire  satisfaction  that 
there  is  no  pus-yielding  pyorrhoea  pocket  about  the  teeth 
which  cannot  be  treated  and  made  perfectly  healthy  by 
the  electrical  introduction  of  ions  into  the  tissues,  pro- 
vided that  the  calculus  deposits  which  are  nearly  always  present 
are  completely  removed.  The  promotion  of  asepsis  in  the 
pockets  is  of  a  permanent  nature  under  favorable  circum- 
stances, and  the  duration  of  cure  depends  on  the  variety 
of  the  disease  and  the  ability  of  the  patient  to  carry  out 
daily  a  regular  system  of  hygiene  of  the  mouth  and  stimu- 
lating the  gums  by  brushing,  etc.    A  few  cases  taken  from 

1  Dental  Surgery  and  Pathology,  p.  630. 


IONIC  MEDICATION 


247 


the  many  hundreds  of  which  accurate  statistics  have  been 
kept,  will  be  stated  in  order  to  make  clear  what  is  implied 
by  the  "cure  of  the  disease." 

Case  A.  On  March  30,  1904,  Miss  L.,  aged  forty-five  years, 
complained  of  a  wide  space  appearing  between  central  lower 
incisors;  teeth  otherwise  perfect.  Examination  revealed 
a  pus-yielding  pocket,  5  or  6  mm.  in  depth,  with  nodules 
of  calculus,  of  hard  dark  variety,  attached  to  the  approxi- 
mal  surface  of  root.  Treatment:  calculus  removed,  root 
polished,  electrical  medication  of  pocket  for  eight  minutes, 
tooth  ligatured  to  next  one  with  silk.  A  week  later  the 
periodontal  membrane  was  perfectly  healthy,  all  pus  had 
disappeared.  The  patient  has  been  .seen  periodically  up 
to  June,  1912.  This  pocket  has  never  been  reinfected  nor 
has  pyorrhoea  appeared  in  other  parts  of  the  mouth.  This 
is  the  easiest  class '  of  septic  periodontal  infection  to  treat 
by  ionization,  it  is  always  readily  cured  provided  the 
displaced  teeth  are  replaced  in  the  normal  position  and 
ligatured  for  a  time.  One  or  two  ionic  treatments  are 
usually  sufficient. 

Fig.  132 


Case  B,  before  treatment. 

Case  B.   On  February  9,  1898,  Miss  P.,  aged  thirty-eight 
years,  six  superior  incisors  protruding,  pyorrhoea  pockets  on 


248 


ELECTRO-THERA  PEUTICS 


palatal  surfaces  extending  to  a  depth  varying  from  1  cm. 
at  the  centrals  to  3  mm.  at  the  cuspids,  teeth  loose  and 
discharge  considerable,  all  other  teeth  slightly  affected,  no 
constitutional  derangement  reported.  Treatment:  all 
calculus  removed  and  protruding  teeth  retracted  (this 
removal  of  calculus  and  replacing  of  displaced  teeth  are 
essential  in  every  case,  and  will  not  be  referred  to  again  in 
describing  treatment),  a  platinum  electrode  with  an  anti- 
septic solution  applied  to  pockets  and  gingival  margins, 
3  to  5  ma.  current,  six  treatments.  At  the  end  of  three 
weeks  all  signs  of  disease  had  disappeared.  The  case  has 
been  seen  once  a  year  up  to  April,  1912,  when  model  was 
taken  (Fig.  133),  the  teeth  were  firm  and  gums  perfectly 
healthy,  the  disease  had  never  recurred. 

Fig.  133 


Case  B,  after  treatment. 


Case  C.  This  case  is  reported  in  the  British  Dental  Journal, 
January,  1899,  p.  2,  and  in  the  Proceedings  of  the  Royal 
Society  of  Medicine,  April,  1908,  and  will  be  briefly  men- 
tioned as  a  bad  case  of  pyorrhoea  which  has  been  cured 
for  fourteen  years.  Miss  R.,  aged  twenty-nine  years,  con- 
sulted me  in  January,  1898,  by  her  doctor's  advice  to  have 
all  her  teeth  extracted.  History  of  thumb  sucking  and 
mouth  breathing  as  a  child.     Superior  incisors  protruding 


IONIC  MEDICATION 


249 


nearly  2  cm.  over  the  inferior  incisors.  Pyorrhoea  pockets 
on  palatal  aspect  of  superior  incisors,  extended  nearly  to  the 
apices,  pockets  of  varying  depth  about  every  tooth  in  the 
mouth  with  considerable  discharge  of  pus.  Teeth  exceed- 
ingly loose  except  molars.  The  patient  was  nervous  and 
debilitated,  suffering  from  alimentary  toxemia.  Treatment: 
loose  bicuspid  extracted,  superior  incisors  retracted.  Pyor- 
rhoea pockets  treated  with  electric  current  with  sulphate  of 
copper  and  iodine.  In  eight  weeks  the  pyorrhoea  had  com- 
pletely disappeared,  but  retraction  of  the  incisors  occupied 

Fig.  134 


Case  C.  before  treatment. 


about  four  months  longer  during  which  time  the  case  was 
seen  only  once  a  month  and  the  treatment  continued.  The 
teeth  are  retained  by  wire  arch  attached  to  a  plate  worn  at 
night  only.  In  1912  the  mouth  presented  the  appearance  of 
the  model  in  Fig.  135.  The  pyorrhoea  has  never  returned  in 
any  part  of  the  mouth,  the  teeth  have  been  cleaned  twice  a 
year  regularly,  but  only  a  few  further  treatments  with  ions. 
The  general  health  of  the  patient  improved  to  a  remarkable 
extent,  and  she  now  possesses  a  useful  strong  set  of  teeth. 

These  three  cases  were  treated,  at  the  time  expecting 
cataphoric  effects,  but  iodine  and  copper  were  used  with  the 


250 


ELECTRO-THERA  PE  U  TICS 


anode  and  cathode,  and  the  writer  now  thinks  the  results 
obtained  were  due  to  penetration  of  ions. 


Fig.   135 


Case  C,  after  treatment. 


Case  D.  Mrs.  H.,  aged  forty-five  years;  every  tooth  of 
otherwise  perfect  set  affected,  pockets  especially  deep  about 


Fig.  136 


Fig.  13; 


Figs.  136  and  137.— Case  D.    X-ray  of  alveolus. 

the  upper  and  lower  molars  where  discharge  was  greatest. 
Teeth  loose  and  patient's  general  health  affected.  X-ray, 
Fig.  136,  shows  condition  of  the  alveolus.     The  case  first 


IONIC  MEDICATION 


251 


treated  April,  1907,  twelve  treatments  with  zinc  ions.  In 
five  weeks  the  symptoms  of  the  disease  had  entirely  disap- 
peared. After  this  one  treatment  a  month  was  given  until 
December  15,  when  the  case  was  discharged  cured.  Since 
that  date  the  patient  has  been  seen  twice  a  year  and  no 
recurrence  of  septic  infection  has  occurred. 

Fig.  138 


Case  E,  before  treatment. 


Case  E.  Mr.  C,  aged  fifty-five  years,  sent  by  a  dental 
friend  on  October  7,  1907.  Nearly  all'  molars,  upper  and 
lower,  lost  from  pyorrhoea,  the  incisors  had  suppurating 
pockets  on  the  palatal  and  approximal  surface;  patient's 
health  affected.  Teeth  very  loose.  Treatment:  eight  treat- 
ments with  zinc  ions  extending  until  December  19,  when 
the  periodontal  membrane  was  perfectly  healthy ;  teeth  firm, 
and  patient's  health  perfectly  restored.  The  case  has  been 
seen  twice  a  year  since,  during  which  time  there  has  been 
no  recurrence  of  pyorrhoea.  The  teeth  were  retracted  to 
their  normal  positions,  as  shown  in  Fig.  139  taken  five  years 
later. 

These  are  a  few  of  hundreds  of  cases  which  could  be 
detailed,  but  it  will  suffice  to  quote  these  typical  ones. 

It  is  perfectly  certain  that  in  most  of  the  cases  here 


252 


ELECTRO-  THERA  PE  VTICS 


stated  that  such  treatment  as  syringing  the  pockets  or 
other  forms  of  irrigation  would  be  quite  inadequate  to 
sterilize  the  tissues  infected  with  pus-yielding  micro-organ- 
isms. It  is  true  that  replacing  teeth  when  displaced  by 
the  disease,  is  in  itself  a  great  aid  in  ordinary  treatment, 
but  this  is  not  sufficient  to  bring  about  a  cure. 

Fig.  139 


Case  E,  five  years  later. 


The  Zinc  Ion. — The  ion  which  appears  to  be  the  most 
sure  and  effective  in  sterilizing  septic  periodontal  membrane 
and  other  forms  of  dental  treatment,  is  the  zinc  ion.  Of 
this  ion  Leduc1  says:  "This  ion  is  an  antiseptic  of  the  first 
rank,  and  when  applied  electrically  it  can  be  made  to 
penetrate  the  tissues  of  the  skin  to  any  desired  depth. 
There  is  no  wound  or  ulcer  which  cannot  be  disinfected  by 
its  employment,  provided  its  surface  can  be  reached  by 
the  electrodes."  This  being  so,  what  form  of  treatment 
for  infected  pyorrhoea  pockets  can  be  more  suited  to  obtain 
that  result  which  it  is  generally  admitted  is  the  chief 
object  in  treatment  of  this  disease?  Every  surface  of  the 
infected  area  can  be  reached  by  proper  electrodes  applied 
direct  to  it.  The  penetration  of  ions  into  periodontal 
tissue  is  easier  than  through  the  skin,  only  a  small  current 

]"  Lesions  en  Medecine,"  Arch.  d'Elect.  Medi.,  September  25,  1904. 


IONIC  MEDICATION  253 

strength  being  necessary,  and  trophic  effects  are  never 
discernible  from  zinc  ions  which  are  well  tolerated  by  the 
tissues. 

The  Copper  Ion. — The  copper  ion  has  also  a  strong 
antiseptic  effect  and  answers  very  well  for  treatment  of 
periodontal  affections;  copper  electrodes  have  the  advantage 
of  being  readily  soluble  by  the  electrolytic  effect  of  the 
current,  even  a  very  small  current  of  1  ma.  seems  to  readily 
cause  dissociation  of  ions,  a  weak  solution  of  copper  sul- 
phate provides  a  solution  electrode  which  produces  the 
ion.  The  copper  ion  is  particularly  useful  for  fistulous 
tracts  such  as  are  often  found  in  the  mouth,  because  a 
copper  probe  is  easily  introduced  into  them,  a  zinc  elec- 
trode being  often  too  rigid  and  too  large  to  enter  the  sinus 
without  enlarging  it. 

The  Iodine  low.— The  iodine  ion  is  distinctly  useful,  and 
while  possibly  not  so  antiseptic  as  the  zinc  ion,  seems  to 
have  a  healing  effect  on  the  tissues.  This  ion  is  indicated 
when  the  tissues  are  nearly  normal  after  a  prolonged  treat- 
ment with  the  zinc  ion,  also  in  treatment  of  the  gingival 
trough,  in  suspicious  cases  of  threatened  pyorrhoea  when 
septic  infection  has  not  yet  caused  the  perceptible  affection 
of  the  periodontal  membrane.  Many  cases  of  periodontal 
disease  can  be  averted  by  treatment  with  this  ion. 

The  Silver  Ion. — The  silver  ion  is  effective  in  the  treat- 
ment of  pulp  canals,  especially  of  molars,  where  the  staining 
properties  of  silver  nitrate  from  which  the  ion  may  be 
obtained,  does  not  matter;  it  is,  however,  more  difficult  to 
handle  in  the  mouth  owing  to  the  caustic  properties  of  the 
drug  before  the  current  is  passed.  It  loses  its  caustic 
properties  by  the  electrolytic  action.  It  is  also  a  useful 
ion  for  obtunding  sensitive  dentine  of  the  exposed  necks 
of  molars  or  cementum  of  roots  of  teeth. 

Argyrol,  a  preparation  of  silver,  possesses  a  distinctly 
sedative  and  soothing  effect  on  gingival  tissue  when  elec- 
trically applied.  A  solution  of  argyrol  can  be  applied  to 
the  tissues  without  staining  or  caustic  effects,  and  is  useful 
in  cases  of  hypersensitive  gingivitis  and  sloughing  of  the 


254  ELECTRO-THERAPEUTICS 

papilla  of  the  interspaces  of  the  teeth.  Argyrol,  however, 
is  a  colloid  preparation  and  ions  do  not  migrate  readily 
if  at  all,  but  the  therapeutic  effect  seems  constant  and  is 
worthy  of  application  even  if  ions  are  doubtful  in  this 
instance. 

The  Cocaine  Ion. — This  is  readily  introduced  into  the 
dentine  of  tooth  structure  by  the  current;  any  of  the  com- 
pound preparations  of  this  drug  act  rapidly  in  producing 
anaesthesia  of  live  teeth.  It  can  be  introduced  into  the 
structure  of  a  tooth  through  a  tiny  opening,  such  as  can  be 
made  by  the  finest  spear  drill  which  will  drill  through 
enamel.  As  soon  as  sensitive  dentine  is  exposed  the  cocaine 
ion,  with  a  current  strength  of  0.5  to  1  ma.,  will  anaesthetize 
the  dentine  in  a  few  minutes,  making  it  possible  to  drill 
nearly  to  the  pulp,  when  a  further  application  will  anaes- 
thetize the  pulp,  so  that  it  can  be  removed  painlessly. 
The  writer  has  only  limited  experience  with  cocaine  ions 
on  soft  tissues,  fearing  the  toxic  effects  that  might  be  pro- 
duced by  rapid  introduction  of  the  ion  is  so  good  a  con- 
ducting medium,  but  Leduc  says:  "The  ion  of  cocaine 
introduced  by  electrolysis  produces  effects  very  different 
from  those  of  a  solution  of  the  same  drug  injected  sub- 
cutaneously.  It  produces  anaesthesia,  but  it  does  not 
diffuse,  and  the  anaesthesia  remains  strictly  limited  to  the 
surface  covered  by  the  electrode.  It  would  appear  that 
the  ion  is  introduced  by  electrolysis,  not  into  the  circula- 
tion, but  into  the  plasma  of  the  cells."  This  opinion,  how- 
ever, was  negatived  in  one  case  in  the  author's  experience, 
in  which  severe  cocaine  poisoning  occurred  when  a  very 
small  dose  of  cocaine  was  introduced  with  the  current 
into  injured  periodontal  tissue,  "in  attemptimg  to  anaesthetize 
the  exposed  pulps  of  a  fractured  tooth.  Other  cases  of  toxic 
effect  of  cocaine  have  been  reported  in  American  journals  in 
which  the  effect  was  produced  through  the  pulp  alone  with 
the  current. 

The  Adrenalin  Ion. — This  is  readily  introduced  into 
the  tissues  affecting  the  vascular  system  in  the  immediate 
area  of  application  of  the  anode,  in  a  very  short  time,  pro- 


IONIC  MEDICATION  255 

during  the  characteristic  anemic  appearance.  The  introduc- 
tion of  the  drug  by  electrolytic  method  shortens  the  time 
required  to  produce  the  effect  of  blanching  the  tissues. 

The  Salicylic  Ion. — This  is  said  to  have  remarkable 
effects  on  facial  neuralgia;  cases  which  have  resisted  many 
other  methods  of  treatment  have  been  reported  cured  by 
introduction  of  this  ion  into  the  affected  area.  Lewis 
Jones1  says  about  trigeminal  perineuritis:  "I  have  had  a 
number  of  complete  successes  in  the  treatment  of  this 
condition  with  salicylic  ions,  and  in  general  the  results 
are  so  good  that  probably  this  has  been  the  experience  of 
all  who  have  tried  it."  Leduc,2  Dawson  Turner,3  and  many 
others  have  published  remarkable  results  in  the  treatment 
of  neuralgia  with  salicylic  ions. 

There  are,  no  doubt,  a  number  of  ions  which  have  not 
yet  been  tried  which  will  be  found  therapeutically  of  great 
value,  those  already  mentioned  have  been  tested  and  their 
effects  properly  demonstrated. 

This  method  of  treatment  is  within  the  reach  of  all 
practitioners,  the  apparatus  which  has  already  been  de- 
scribed in  other  parts  of  this  work  is  simple,  inexpensive, 
and  readily  obtained;  the  technique  is  not  nearly  as  difficult 
as  many  kinds  of  special  work  carried  out  by  dentists. 
Thorough  knowledge  of  the  electrical  phenomena  appli- 
cable to  electro-therapeutics  is  essential  or  the  worker 
is  liable  to  be  puzzled  by  minor  phases  of  the  action  of 
the  current,  which  might  interfere  with  persevering  with 
the  method,  whereas  when  these  are  thoroughly  under- 
stood, they  are  seen  in  their  proper  light  and  avoided  or 
disregarded  as  of  no  vital  importance. 

The  Advantages  of  Ionic  Medication. — The  advantages 
of  ionic  medication  in  dentistry  are  many.  It  is  easily 
carried  out;  it  is  not  nearly  as  painful  as  many  other 
operations;  it  is  effective;  there  are  no  ill  effects;  any  dis- 
comfort caused  at  the  time  of  administration  disappears 

1  British  Medical  Journal,  August  31,  1912,  p.  488. 

-  Arch.  d'Elect.  rued.,  1904. 

3  British  Medical  Journal,  April  4,  1908. 


256  ELECTRO-THERAPEUTICS 

the  instant  the  current  is  turned  off;  improvement  is  notice- 
able at  once  and  is  unmistakable  by  patient  and  operator; 
it  places  at  our  disposal  a  method  of  applying  antiseptics, 
sedatives,  stimulants,  or  styptics  to  a  local  area  which  act 
in  concentration  on  the  part  medicated. 

Effect  of  Ions  on  Bacteria. — The  immediate  effects  of 
passing  an  antiseptic  ion  such  as  zinc,  copper,  silver,  or 
iodine  into  an  electrolyte,  such  as  an  area  of  periodontal 
tissue  or  a  septic  pulp  canal,  is  the  destruction  of  the  micro- 
organisms contained  in  the  area  through  which  the  elec- 
trically charged  ions  radiate.  This  effect  has  been  clinically 
demonstrated  by  many  eminent  medical  workers  in  this 
special  branch  of  electro-therapeutics.  The  author  has 
found  that  inflamed  periodontal  tissue,  yielding  pus  from 
infected  pyorrhoea  pockets,  becomes  perfectly  healthy 
when  treated  with  antiseptic  ions.  In  addition  to  this, 
constitutional  symptoms,  which  so  often  accompany  this 
disease,  such  as  general  malaise,  headache,  indigestion, 
anemia,  laryngitis,  pharyngitis,  acneiform  eruptions,  and 
some  forms  of  alimentary  toxemia,  subside  and  disappear 
altogether  when  they  are  caused  (as  they  often  are)  by 
the  absorption  in  the  general  circulation  of  the  products 
of  chronic  suppurative  conditions.  It  has  been  pointed 
out  by  exponents  of  vaccine  therapy  that  the  pus  ob- 
tained from  suppurating  periodontal  membrane  contains 
a  great  variety  of  species  of  bacteria,  that  they  are  also 
found  in  the  tissues  of  the  affected  area.  Simms,1  Goadby,2 
Ayre  and  Payne3  have  enumerated,  staphylococcus  albus 
and  aureus,  streptococcus  brevis  and  longus,  micrococcus 
catarrhalis,  spirilla  and  bacillus  fusiformi  and  many  other 
micro-organisms  but  no  specific  organism.  In  administer- 
ing vaccine  prepared  from  organisms  obtained  from  pyor- 
rhoea infection,  the  predominating  organism  or  a  mixture 
of   organisms   are   employed   with    the   hope  of   stimulat- 

1  "  Observations   on   the   Bacteriology   of   Pyorrhea   Alveolaris,"    Trans. 
Odont.  Soc.  Great  Britain,  1907,  xxxix,  p.  164. 

2  Trans.  Odont.  Soc.  Great  Britain,  xxxvii,  p.  145. 

3  Proc.  Royal  Soc.  Med.  (Odont,  Sect.),  December,  1909. 


IONIC  MEDICATION  257 

ing  the  production  of  antibodies  (opsonins)  of  the  corre- 
sponding variety  to  those  responsible  for  the  pathological 
condition  existing  and  to  render  the  patient  immune  by 
the  injection  of  killed  cultures  of  the  suspected  organism  or 
organisms. 

It  is  with  a  certain  amount  of  diffidence  that  the  author 
ventures  to  make  the  suggestion  (not  having  investigated 
the  subject)  that  by  the  destruction  of  micro-organisms 
in  suppurative  periodontal  tissue,  by  ionization,  the  anti- 
bodies are  provided  by  subsequent  absorption  of  dead 
micro-organisms  into  the  general  circulation.  It  is  further 
obvious  that  if  these  micro-organisms  in  the  tissues  are, 
in  their  active  state,  responsible  for  the  general  systemic 
disorders  accompanying  the  disease,  that  the  right  organ- 
isms will  always  be  provided,  there  will  be  no  mistake  on 
that  point.  The  question  arises  whether  the  numbers  of 
living  bacteria  to  be  found  in  the  tissues  and  destroyed 
there  by  the  ionic  treatment  are  sufficiently  large  to  affect 
the  opsonic  index. 

However  this  may  be,  it  is  a  fact  that  constitutional 
disorders  which  have  arisen  from  the  effects  of  existing 
chronic  pyorrhoea  alveolaris  usually  disappear  when  the 
disease  has  been  treated  by  ionic  medication,  and  locally 
the  tissues  are  restored  to  normal  condition.  Malaise  will 
nearly  always  disappear  before  the  disease  can  be  said  to  be 
cured.  This  is  a  frequent  experience  of  the  writer  in  cases 
which  have  come  under  his  notice. 

It  has  been  demonstrated  experimentally  by  Brewer, 
Zierler,  Letronaum,  and  others  that  the  passing  of  a  cur- 
rent alone  has  a  sterilizing  effect  on  cultures  of  bacteria 
in  agar,  and  Zierler  reports  having  put  this  into  practice 
for  sterilizing  root  canals,  using  small  current  of  3  or  4 
milliamperes,  with  satisfactory  results. 

Bethel  has  also  shown  that  micro-organisms  infecting  pulp 
canals  can  be  destroyed  by  passing  a  current  with  nitrate 
of  silver  as  the  solution  electrode,  in  which  he  doubtless 
obtained  silver  ions,  but  he  attributes  the  effect  to  a  com- 
bination of  electrolysis  and  cataphoresis. 
17 


258  ELECTRO-THERAPEUTICS 

Hoffendale  also  published  similar  effects  on  bacteria 
in  the  treatment  of  root  canals  with  the  current. 

Josef  Peter1  has  published  his  clinical  experience  in  the 
same  direction  with  the  current  and  states  that  "the  result 
was  excellent  in  every  case." 

The  author  has  used  ions  of  zinc,  silver,  copper,  or  iodine 
for  a  number  of  years;  he  rarely  fills  a  pulp  canal  without 
subjecting  it  to  ionic  treatment.  Ions  of  zinc  seem  to  be 
the  most  effective,  a  perfect  sterilization  of  the  canal  walls  is 
effected  and  septic  disturbances  after  filling  of  the  roots  is 
practically  impossible  if  this  operation  is  carried  out  with 
due  care. 

1  Dental  Cosmos,  vol.  xlvii,  p.  1136. 


CHAPTER  XI. 

TECHNIQUE  OF  IONIC  MEDICATION  IN  DENTAL 
OPERATIONS. 

When  a  continuous  current  from  the  main  is  used,  the 
chair  in  which  the  patient  is  seated  must  be  insulated 
from  all  contact  with  earth.  Most  dental  chairs  have  a 
large  amount  of  metal  about  them  and  if  they  rest  on 
wooden  or  even  carpeted  floors  fairly  good  contact  with 
earth  may  be  established,  especially  in  very  damp  weather. 
A  perfect  insulation  is  effected  by  resting  the  metallic  base 
of  the  chair  on  a  rubber  mat. 

Water  pipes  or  gas  fixtures  should  not  be  within  reach 
of,  or  be  touched  by,  either  patient  or  operator  when  the 
current  is  being  used. 

Metallic  supports  for  cuspidors  must  not  be  touched  if  in 
contact  with  earth. 

Saliva  ejector  must  not  be  used  with  the  patient  in  elec- 
trical contact;  there  is  only  a  slight  chance  of  contact  with 
earth  being  established  in  this  way,  but  it  is  best  not  to 
take  the  chance. 

A  continuous  current  either  from  a  switchboard  described 
(p.  125)  or  from  a  voltic  cell  battery  (p.  95)  is  the  proper 
current  for  ionic  medication. 

The  current  at  the  starting  point  (zero)  should  be  less 
than  0.1  milliampere.  It  must  be  so  regulated  by  resistance 
in  circuit  that  it  can  be  increased  in  E.  M.  F.  and  in  current 
strength  by  not  more  than  0.1  volt  and  0.1  milliampere  at 
a  time.  Current  collectors  which  switch  on  one  cell  at  a 
time  increase  the  voltage  and  amperage  too  suddenly  and 
should  not  be  used  for  ionization  of  oral  tissues. 


260  ELECTRO-THERAPEUTICS 

A  milliampere  meter  is  essential. 

Conducting  cords  should  be  perfect  and  attached  securely 
to  the  switchboard  or  battery  terminals  and  to  the  elec- 
trodes; loose  moving  contacts  produce  disagreeable  little 
shocks  by  occasional  break  of  current. 

The  active  electrode  (p.  123)  must  be  selected  to  suit  the 
particular  purpose  for  which  ions  are  required.  In  pyor- 
rhoea treatment,  metals  corresponding  to  the  solution  em- 
ployed or  else  of  platinum,  must  be  used ;  platinum  may  be 
used  with  any  solution  as  it  is  not  soluble  itself.  The  area 
and  cross-section  of  an  active  electrode  influences  the 
density  of  the  current.  Very  fine  electrodes  are  painful 
in  periodontal  tissue  even  with  a  small  current;  an  electrode 
of  2  mm.  X  1  mm.  X  4  cm.  tapering  to  the  required  size 
just  large  enough  to  be  admitted  easily  into  the  spaces  or 
pockets  to  be  medicated,  should  be  used. 

The  solutions  should  be  conveyed  to  the  site  of  medica- 
tion on  absorbent  wool  tightly  wound  about  the  shaft  of 
the  metallic  electrode  conductor,  and  wetted  occasionally, 
as  replenishing  becomes  necessary. 

The  electrode  should  be  placed  in  position  before  raising 
the  current  from  zero,  the  current  should  then  be  gradually 
increased  until  2  to  5  ma.  are  registered  and  the  patient 
indicates  that  a  pricking  sensation  is  felt  in  the  tissues; 
it  should  then  be  reduced  by  0.2  ma.  and  the  electrode  kept 
steadily  in  position  for  from  one  to  live  minutes  according 
to  the  necessity  for  a  large  or  small  dose  of  ions.  It  should 
be  the  object  to  use  as  high  a  current  strength  as  possible 
up  to  15  ma.  without  giving  undue  pain. 

The  soft  tissues  are  less  sensitive  to  current  than  dentine 
at  necks  of  teeth,  the  metal  electrode  should  be  kept  away 
from  sensitive  teeth  as  much  as  possible.  Intervals  of 
treatment  in  pyorrhoea  alveolaris  should  be  three  times 
a  week  for  first  week,  twice  a  week  for  second  and  third 
weeks,  once  a  week  after;  this  should  be  varied  according 
to  the  severity  of  the  case,  it  being  best  to  vigorously  keep 
up  treatment  at  first  until  all  pus  disappears. 

Metallic  fillings  in  live  teeth  should  be  avoided  when 


TECHNIQUE  OF  IONIC  MEDICATION  2G1 

possible.  When  impossible,  small  currents  for  a  longer  time 
should  be  used. 

The  current  should  be  reduced,  to  zero  before  removing 
the  electrode  from  site  of  ionization  or  a  painful  shock  will 
be  experienced. 

Very  little  shocks  are  a  stimulus  and  do  some  good,  they 
may  be  practised  if  the  nature  of  the  patient  permits. 

The  shaft  of  active  electrode  should  be  insulated  or  not 
allowed  to  touch  the  cheek,  lips,  or  tongue. 

The  saliva  should  be  kept  away  by  cotton  rolls  or  napkins. 

Interspaces  of  teeth  and  -pyorrhoea  pockets  should  be  syringed 
with  antiseptic  lotion  before  ionization. 

The  indifferent  electrode  should  be  strapped  to  the  patient's 
wrist  or  held  by  the  patient  or  placed  under  the  chin.  It 
should  always  be  covered  with  lint  or  chamois  skin,  and 
should  be  moistened  with  water  or  a  saline  solution.  If 
the  metallic  indifferent  electrode  causes  blisters  or  smarts 
the  skin,  a  carbon  electrode  in  a  glass  dish  of  tepid  water 
with  a  little  chloride  of  sodium  in  it  should  be  used.  The 
carbon  should  be  covered  with  lint  and  the  patient's  hand 
pressed  firmly  on  it. 

Rings  should  be  removed  from  the  hand  holding  indif- 
ferent electrode. 

Electrodes  should  be  held  firmly  and  contact  over  as 
large  an  area  as  possible  insured. 

The  poles  should  be  tested  in  all  new  switchboards  or 
batteries   (see  p.  42). 

When  acid  radical  ions  are  required,  a  lower  current 
strength  will  be  indicated,  as  the  negative  pole  is  more 
painful  with  small  electrodes  than  the  positive. 

It  is  best  to  begin  with  a  low  voltage  and  current  strength, 
as  it  will  be  found  that  the  resistance  of  the  body  becomes 
less  as  the  seance  goes  on  and  highly  susceptible  patients 
will  stand  more  if  this  precaution  is  observed. 

The  principles  peculiar  to  the  movement  of  ions  referred  to 
on  p.  241  must  be  observed. 

For  anaesthesia  of  dentine  or  ptdp  active  electrodes  of 
as  large  an  area    as    possible    must   be  used.     The  metal 


262  ELECTRO-THERAPEUTICS 

conductor  must  not  be  brought  in  contact  with  the  dentine 
or  pulp;  cotton  wool  saturated  with  the  anaesthetics  should 
first  be  placed  in  the  cavity  and  the  electrode  pressed 
firmly  on  this.  The  area  of  the  electrode  can  be  increased 
by  placing  a  piece  of  platinum  foil  over  the  wool  and 
attaching  the  electrode  to  this. 

Resistance  in  dentine  is  great,  therefore  the  E.  M.  F. 
required  will  be  great,  and  current  strength  required  much 
less  than  in  dealing  with  soft,  moist  tissue;  0.5  ma.  will 
sometimes  be  painful  but  this  amount  of  current  is  often 
sufficient  to  anaesthetize  dentine,  or  it  may  be  raised  to  1  or 
2  ma.  after  a  few  minutes'  seance.  When  the  pulp  becomes 
anaesthetized  a  current  of  3  or  4  ma.  will  give  no  sensation, 
and  this  is  a  sign  that  the  pulp  may  be  drilled  into  without 
any  pain. 

For  sterilizing  pulp  canals,  the  electrode  of  fine  platinum 
wire,  or  steel  nerve  canal  instrument  should  be  passed 
into  the  canal  or  canals,  a  solution  of  antiseptic  to  be  used 
must  be  introduced  into  the  cavity  on  cotton  wool,  the 
saliva  kept  away,  an  active  electrode  must  be  connected 
to  the  electrode  in  situ,  and  current  of  3  to  5  ma.  allowed 
to  pass  for  5  minutes.  The  resistance  of  dead  teeth  is  very 
great  and  often  very  little  current  will  pass. 

For  treatment  of  fistulous  tracts,  a  soluble  copper  electrode 
should  be  passed  into  the  fistula  and  to  this,  in  situ,  a 
platinum  or  copper  active  electrode  connected.  A  current 
of  3  to  5  ma.  is  usually  bearable.  Five  minutes  will  furnish 
a  dose  of  copper  ions  sufficient  to  sterilize  the  tract.  The 
pulp  canal  should  be  sterilized  also  as  above  described. 
The  soft  tissues  will  adhere  firmly  to  the  electrode;  it  should 
not  be  forcibly  removed,  the  tissues  will  relax  their  hold 
in  a  short  while,  and  if  not,  reverse  the  poles  and  pass  a 
negative  current  for  about  half  a  minute,  this  will  loosen 
the  electrode. 

For  bleaching  discolored  teeth,  a  platinum  electrode 
should  be  used  and  the  patient  can  hold  the  indifferent 
electrode,  or  the  more  effective  method  is  to  place  the  two 
electrodes  pf  platinum  wire  in  the  tooth,  separated  there 


TECHNIQUE  OF  IONIC  MEDICATION  263 

by  as  far  a  space  as  circumstances  will  allow  and  interpose 
cotton  wool  saturated  with  the  bleaching  compound  in 
solution. 

Care  must  be  taken  not  to  short  circuit  the  current 
either  within  the  tooth  or  without  by  allowing  electrodes 
or  wires  to  meet.  By  this  method  with  fine  electrodes  5  ma. 
current  produce  some  heat,  10  to  15  ma.  produce  intolerable 
heat  in  the  tooth. 

The  tooth  should  be  isolated  by  applying  rubber  dam. 
Metallic  fillings  should  be  removed.  Fine  platinum  wire 
electrodes  produce  more  heat  than  thick  wires.  The  poles 
should  be  reversed  with  the  electrode  in  situ,  when  the 
operator  is  about  half  completed.  Heat  is  increased  by 
permitting  the  cotton  wool  interposed  between  the  elec- 
trodes to  become  slightly  dry 


CHAPTER  XII. 
HIGH  FREQUENCY  AND  STATIC  CURRENTS. 

X-ray  and  High  Frequency  Currents. 

These  currents  are  much  used  in  medical  electricity 
for  general  electrification  of  the  body,  and  for  local  appli- 
cation. The  effects  are  of  a  mixed  character,  acting  largely 
on  the  nervous  system,  circulation,  respiration,  and  as 
D'Arsonval  has  shown,  on  micro-organisms. 

Therapeutically  these  currents  are  applied  in  many 
special  ways  for  treatment  of  diabetes,  gout,  rheumatism, 
tuberculous  glands,  neuralgia,  pyorrhoea,  and  many  other 
local  and  general  diseases.  Mr.  L.  C.  Creasy1  advocates  a 
special  form  of  static  application  for  treatment  of  glands 
which  are  enlarged  by  the  absorption  of  toxins  from  the 
teeth — lymphadenitis.  This  he  terms  Intensive  Irradiation 
and  Static  Wave  Treatment.  The  treatment  consists 
in  first  treating  the  affected  area  by  intensive  irradiation 
from  a  500  candle-power  incandescent  lamp  with  special 
reflecting  properties,  this  increases  local  metabolism  and 
elimination.  The  static  wave  current  is  then  applied  with 
the  object  of  increasing  physiological  resisting  power  of  the 
parts.  "Passive  congestions  are  removed  by  improving  the 
physiological  'tone'  of  the  affected  region." 

This  method  of  applying  the  static  wave  current  is  best 
described  by  quoting  the  words  from  that  author  who 
quotes  Potts:  "The  patient,  on  an  insulated  platform, 
must  be  connected  to  the  side  of  the  static  machine  that 
is  not  grounded.    The  electrodes  should  be  of  pliable  metal 

1  L.  C.  Creasy,  M.R.C.S.,  L.R.C.P.  The  Practitioners'  Encyclopedia  of 
Medicine  and  Surgery. 


HIGH  FREQUENCY  AND  STATIC  CURRENTS      265 

and  the  treatment  should  be  commenced  with  the  prime 
conductors  practically  closed.  On  drawing  the  prime  con- 
ductors apart  the  wave  current  will  become  apparent  and 
as  wide  a  spark  should  be  used  as  can  be  easily  tolerated 
by  the  patient." 

This  form  of  treatment  for  glands  affected  by  toxins 
from  teeth  or  gums  is  a  distinct  advance  on  anything  so 
far  recommended  outside  of  surgical  treatment  for  acute 
and  chronic  lymphadenitis. 

Much  controversy  has  arisen  as  to  how  these  glands  are 
affected,  and  as  to  the  correct  diagnosis  of  lymphadenitis, 
but  outside  of  aseptic  oral  treatment  nothing  seems  to  have 
been  recommended  for  treatment  in  chronic  cases. 

High  frequency  currents  have  attracted  little  attention. 
They  have,  however,  been  used  on  the  Continent  with 
considerable  success  in  the  treatment  of  acute  periodontal 
disease.  It  is  claimed  that  this  oscillating  current  has  an 
ionic  effect  on  solution  electrodes  placed  on  the  tissues. 

Dr.  William  Dunn,  of  Florence,  has  pointed  out  that 
high-frequency  currents  possess  valuable  therapeutic 
properties  which  are  singularly  adapted  to  the  treatment 
of  pyorrhoea  alveolaris.  He  points  out  that  the  stimulat- 
ing, antiseptic,  and  antitoxic  properties  of  high-frequency 
currents  are  especially  indicated  in  the  treatment  of  dis- 
eased tissues  in  which  the  pathological  conditions  are 
accompanied  with  depressed  or  lost  vitality  or  with  a 
disturbance  of  metabolic  functions.  Together  with  his 
colleague,  Dr.  Luigi  Arnone,  of  Florence,  good  results  are 
claimed  from  high-frequency  treatment  of  pyorrhoea,  using 
the  currents  as  an  auxiliary  after  surgical  treatment  of  the 
disease,  he  says,  "In  every  case  with  marked  beneficial 
effects,  the  gums  toning  up  and  looking  healthy  and  hard 
in  a  short  time,  pus  ceasing  more  rapidly  than  before, 
and  the  teeth  bracing  up  rapidly."  Dr.  Dunn  also  puts 
forward  the  anaesthetic  effects  of  high-frequency  currents 
in  dental  treatment,  pointing  out  the  great  usefulness  of 
this  property  of  these  currents  in  cases  where  cocaine  is 
contra-indicated,  he  says,  "sufficient  anaesthesia  has  been 


266  ELECTRO-THERAPEUTICS 

obtained  locally  to  perform  painlessly  some  of  the  minor 
operations,  such  as  lancing  gums,  removing  roots,  etc." 
Other  workers  in  this  special  electrical  branch  have  re- 
ported successful  anaesthetic  effects  from  high-frequency 
currents,  among  them  Dr.  Didabury  claims  a  high  degree 
of  success. 

A  form  of  high-frequency  treatment  which  is  called  by 
the  author,  Monsieur  F.  Morel,1  of  Dreux,  "Alto-frequent 
effluvation,"  has  been  described  by  him  as  having  remark- 
able effects  in  the  treatment  of  pyorrhoea  alveolaris  by  the 
formation  of  what  he  terms  "mixions."  In  the  following 
description  of  the  action  of  these  currents  he  says:  "This 
effluvolysis  does  not,  like  electrolysis,  have  for  its  result 
a  simple  transport  of  the  ions  which  travel  respectively 
toward  the  positive  or  the  negative  pole,  but  there  is 
produced  in  consequence  of  the  frequent  periods,  molec- 
ular vibrations  to  which  these  periods  give  rise — vibrations 
which  constitute  a  veritable  ionic  bombardment.  It  is 
no  longer  a  question  merely  of  cathions  or  anions;  all  these 
ions  clash  together,  mix,  unite,  and  combine  to  form  new 
molecules  of  a  different  chemical  formula  from  the  primi- 
tive element.  The  exchange  of  the  ions  is  cathodic  and 
anodic  at  the  same  time  at  the  point  of  application  of  the 
effluves;  I  will  call  the  molecules  thus  newly  formed 
'mixions.'  " 

Monsieur  Morel  states  that  he  has  experimentally  intro- 
duced ions  into  the  bodies  of  animals  by  this  method  of 
alto-frequent  effluvation  and  produced  in  them  therapeutic 
effects  characteristic  of  the  ion  used,  cyanide  of  potassium 
and  oxalate  of  strychnine  producing  convulsions  and  death 
to  guinea-pigs. 

Regarding  the  action  of  the  ions  formed  by  the  efflu- 
volysis of  bichromate  of  potash  he  gives  the  following 
formula : 


0  .,  .        Cr 


CrO 


Cr207K2  +  4H20  =  anions  —  +  cathions  =  mixions  HO 


H     '  K 


KOH 


1  Bulletin  du  Syndicat  des  Chirugien-Dentistes  de  France. 


HIGH  FREQUENCY  AND  STATIC  CURRENTS       267 

which  shows  that  the  chemical  composition  of  the  bichro- 
mate of  potash  and  water  is  changed  by  the  effluvolytic  ioni- 
zation into  chromic  acid  (2Cr02)  +  caustic  potash  (2KOH) 
+  water  (H20)  and  for  them  he  claims  antiseptic  and 
stimulating  effects  from  the  chromic  acid,  and  solvent  prop- 
erties on  tartar  for  the  caustic  potash.  The  effect  he  claims 
is  a  perfect  medication  of  "mixions"  which  are  not  elimin- 
ated from  the  tissues  for  some  days ;  he  states  that  "  urologic 
analysis  does  not  reveal  to  us  the  presence  of  the  medica- 
ment until  twelve  hours  after  effluvation,  and  does  not 
become  eliminated  before  the  end  of  two  days." 

In  addition  to  the  antiseptic  effect  of  the  ions,  a  stimu- 
lating effect  in  the  protoplasm  of  cells  is  produced  and  a 
further  antiseptic  effect  from  the  production  of  ozone  at 
the  contact  of  the  electrode. 

The  technique  of  this  method  of  treatment  is  briefly  as 
follows : 

The  gums  or  necks  of  affected  teeth  are  painted  with  a 
solution  of 

Fluosilicate  of  soda 2  gms. 

Chloride  of  ammonia 1  gm. 

Chloride  of  potassium 11  gms. 

Salicylate  of  theobromine  ........        1  gm. 

Methylal 50  cgms. 

Distilled  water 20  gms. 

Filter. 

A  pad  of  cotton  wool  saturated  with  a  solution  of  bichro- 
mate of  potash  in  water  1  to  10  is  placed  over  the  necks 
of  4  teeth  at  a  time  and  on  this  pad  is  placed  the  empty 
electrode  of  the  alto-frequent  current;  this  is  pressed  firmly 
but  not  roughly  into  place,  and  an  "alto-frequent  rain  of 
effluves"  is  passed  into  the  tissues. 

In  advanced  pyorrhoea  cases  a  metallic  electrode  is 
used  which  projects  about  ten  sparks  in  the  infected 
pockets.  The  operation  of  effluvation  lasts  for  five  minutes 
at  a  time  and  three  such  are  given;  this  is  repeated  every 
two  days  for  six  visits.  Metal  fillings  must  be  insulated 
by  covering  them  with  gutta-percha,  to  protect  against 
pain  which  the  current  would  otherwise  cause. 


268  ELECTRO-THERAPEUTICS 

X-ray  and  High  Frequency  Currents. — From  time  to  time 
reports  have  been  made  in  the  journals  of  the  good  results 
obtained  by  the  combined  use  of  .r-ray  and  high  frequency 
currents  in  the  treatment  of  pyorrhoea  alveolaris.  Dr. 
C.  H.  Parker,1  of  Chicago,  in  1903,  advocated  the  use  of 
.r-ray  for  one  or  two  minutes  and  then  high  frequency  for 
five  minutes,  having  previously  sprayed  the  affected  gums 
with  a  mixture  of  iodine,  aconite,  myrrh,  and  wintergreen. 
He  says :  "  The  object  of  spraying  the  gums  with  medicament 
before  turning  on  the  z-ray  and  high  frequency  currents 
on  the  patients  is  to  have  the  chemicals  carried  into  the 
tissues  by  these  currents."  His  method  of  applying  the 
high  frequency  electrodes  over  the  mouth  of  the  patients 
also  has  the  effect  of  saturating  the  tissues  with  ozone 
which  by  its  high  oxidation  properties  increases  metab- 
olism and  elimination  with  consequent  improvement  in 
the  condition  of  stasis  which  attends  the  disease.  From 
this  method  of  treatment  very  good  results  were  obtained. 

Dr.  F.  Le  Roy  Satterlee,  Jr.,2  of  New  York,  improved 
on  the  method  of  applying  the  high  frequency  currents  to 
pyorrhoea  teeth  by  applying  the  vacuum  electrode  directly 
to  the  gums,  and  agrees  with  Dr.  Parker  on  the  results 
obtained  by  this  treatment,  he  says;  "This  treatment  in 
combination  with  .r-ray  has  proved  very  successful  in  a 
number  of  cases,  and  in  the  early  stages  of  pyorrhoea 
where  the  alveolus  has  not  been  entirely  sloughed  away 
we  may  claim  a  complete  cure,  the  teeth  tighten  up,  with 
restoration  of  the  gums  to  a  healthy  condition."  Two 
years  later  Dr.  Le  Roy  Satterlee,3  after  further  testing  the 
use  of  a-ray  and  high  frequency  currents  in  the  treatment 
of  pyorrhoea,  says:  "I  have  derived  the  best  results  from  a 
combination  treatment  of  .r-ray  and  the  use  of  special 
vacuum  electrode  of  my  own  design  that  conveys  the 
high  frequency  currents  and  at  the  same  time  bathes  the 
gums  and  underlying  tissues  in  the  rich  radiations  of  the 
bi-ultra-violet  rays.     A  metal  electrode  is  meanwhile  held 

1  Dental  Cosmos,  vol.  xlv,  p.  947. 

2  Ibid.,  vol.  xlvi,  p.  642.  3  Ibid.,  vol.  xlviii,  p.  274. 


X-RAY  AND  HIGH  FREQUENCY  CURRENTS      269 

in  the  hand  to  complete  the  circuit  through  the  body  of 
the  D'Arsonval  currents." 

S.  Tousey,1  of  New  York,  advocates  a  combination  of 
x-ray  and  high  frequency  currents  for  the  treatment  of 
pyorrhoea  alveolaris.  A  specially  prepared  ar-ray  tube  with 
the  ray  localized  to  an  opening  in  a  shield  of  2\  inches 
is  used.  "The  rays  should  be  about  No.  4  of  the  Walter 
or  of  the  Benoist  scale,  the  resistance  equal  to  a  parallel 
spark  of  about  2  inches,  the  primary  current  about  3  am- 
peres, with   a    12-inch  coil  and  Wehnelf   interrupter   and 

Fig.  140 


Tousey's  x-ray  tube  for  treating  pyorrhea. 

a  current  of  2  ma.  passing  through  the  jc-ray  tube. 
The  anticathode  of  the  tube  is  about  10  inches  from  the 
face,  the  lips  are  open,  exposing  the  teeth  and  gums,  and 
the  time  of  exposure  is  from  one  to  two  minutes."  The 
a>ray  escapes  only  from  this  special  tube  at  the  end  of 
the  prolongation  and  the  strength  of  application  is  much 
reduced  as  compared  with  the  ordinary  ic-ray  tube.  Treat- 
ments are  given  to  the  affected  gums  twice  a  week, 
immediately  followed  on  each  occasion  by  high  frequency 
currents,  applied  by  vacuum  electrodes  especially  prepared 


1  Medical  Electricity  and  Rontgen  Rajs,  p.  566. 


270  ELECTRO-THERAPEUTICS 

for  this  purpose,  which  fit  the  different  aspects  of  the 
alveolar  border  and  necks  of  the  teeth.  The  high  frequency 
is  applied  for  thirty  seconds  to  one  place  and  then  moved 
to  another.  The  usual  ozone  effect  is  noticed  about  the 
electrode  and  the  application  is  said  to  be  entirely  painless. 

Tousey  says:  "The  results  are  very  prompt  relief  of  pain 
and  improvement  on  the  ulceration,  so  that  in  three  weeks 
the  dentist  almost  always  reports  that  the  teeth  are  better 
than  for  six  months  previously.  The  teeth  gradually 
tighten  up  and  the  tenderness  disappears." 

He  recognizes  that  there  are  many  forms  of  pyorrhoea 
and  that  the  best  results  are  not  obtainable  in  some  forms 
of  the  disease  by  this  combined  axray  and  high-frequency 
method.  Those  cases  which  are  dependent  on  constitu- 
tional complications  would  be  contra-indicated.  It  must, 
however,  be  kept  in  mind  that  the  .r-ray  is  a  very  destructive 
ray  to  tissues  and  too  long  exposure  might  result  in  burns, 
even  with  as  low  a  current  as  here  recommended.  The 
danger  to  which  the  operator  is  constantly  exposed  must 
also  be  remembered,  and  special  attention  is  drawn  to  this 
in  dealing  with  the  technique  of  Dental  Radiography  in 
another  chapter  of  this  work  (p.  183). 


CHAPTER   XIII. 
ELECTRO-THERAPEUTICS  IN  DENTISTRY. 

Treatment  of  Dead  Teeth — Periodontitis  from  Septic  Pulp — Acute 
Local  Periodontitis — Perforation  of  the  Apex — Perforation  of  the  Side 
of  the  Canal — Alveolar  Abscess — Chronic  Alveolar  Abscess — Necrosis  of 
the  Jaws — Marginal  Gingivitis. 

Treatment  of  Dead  Teeth. — We  often  have  to  deal  with 
teeth  in  which  the  pulps  have  died  from  the  effect  of  caries, 
traumatism,  and  numerous  other  causes.  In  these  cases 
suppuration  of  the  pulp  is  very  general  with  sometimes 
periodontitis  of  more  or  less  severity.  On  removing  the 
pulp  it  is  often  found  that  it  is  not  possible  to  reach  the 
apical  foramen  with  a  fine  nerve  instrument  because  the 
root  canal  is  either  constricted  or  tortuous.  The  one  object 
of  all  operators  in  those  cases  is  to  cleanse  and  make  the 
canals  aseptic,  which  is  often  a  difficult  matter  in  molars, 
or  crooked  roots.  This  can  be  readily  done  by  ionic  medi- 
cation with  antiseptic  ions.  The  root  canal  should  not  be 
enlarged  with  reamers;  the  pulp  tissue  or  purulent  matter 
should  first  be  removed  as  well  as  possible,  and  the  canal 
washed  out.  The  canal  should  then  be  filled  with  a  solution 
electrode,  of  which  zinc  chloride  5  per  cent,  solution  is  one 
of  the  most  useful;  a  fine  electrode  of  platinum  or  steel 
should  be  introduced  into  the  canal  to  as  near  the  apical 
foramen  as  it  will  go,  but  should  not  pass  through  it  into 
the  periodontal  tissue.  To  this,  contact  should  be  made 
with  the  anode  from  the  continuous  current,  by  holding 
it  in  position;  the  current  should  be  gradually  turned  on 
and  3  to  5  ma.  passed  for  five  minutes.  This  will  im- 
pregnate the  walls  of  the  tooth  pulp  canal  with  ions  of 
zinc  and  ions  will  also  pass  through  the  foramen  and  render 


272 


ELECTRO-THERAPEUTICS 


the  tract  aseptic.  In  teeth  with  more  than  one  root  an 
electrode  must  be  introduced  into  each  root  and  joined  in 
proper  contact,  where  they  meet  in  the  cavity  or  outside 
the  tooth;  the  current  should  then  be  applied  to  these  as 
before. 

The  action  of  the  current  is  to  permeate  the  hard  tissue 
walls  with  antiseptic  ions  in  a  manner  quite  impossible 
by  osmosis;  furthermore,  the  ions  remain  as  a  permanent 
antiseptic.  The  ionic  effect  is  sure  because  the  current  does 
not  conduct  without  this  electrolytic  effect. 

Fig.  141 


Premolar  with  electrodes  in  position  for  ionization  of  roots. 


I  have  known  cases  in  which  it  has  been  impossible  to 
seal  the  canal  without  the  rapid  formation  of  gases  and 
pain  in  twenty-four  hours,  to  yield  to  ionic  medication  with 
zinc  ions  after  a  single  treatment. 

Miss  W.,  a  doctor's  daughter,  had  a  dead  central  incisor 
which  could  not  be  sealed  for  twelve  hours  without  causing 
pain.  The  attempt  had  been  made  many  times  by  her 
dentist,  who  sent  her  to  me.  The  canal  appeared  clean. 
One  treatment  was  given  with  zinc  ions  from  zinc  chloride 
for  eight  minutes  with  5  ma.  current,  and  the  canal  sealed 
temporarily.  A  week  later  zinc  ions  were  again  introduced 
into  the  canal  as  a  precautionary  measure  and  the  root 


TREATMENT  OF  PERIODONTITIS  273 

permanently  filled.  This  was  done  three  years  ago.  There 
has  been  no  recurrence  of  the  inflammatory  condition, 
which  was  doubtless  a  septic  infection  of  the  periodontal 
membrane  caused  by  bacteria  in  the  root  canal. 

Periodontitis  from  Septic  Pulp. — The  complication  of  acute 
periodontitis  is  sometimes  the  direct  effect  of  septic  pulp 
canal.  This  may  subside  when  the  pulp  canal  is  opened 
and  treated,  but  if  bacteria  are  not  completely  eradicated 
the  recurrence  of  periodontal  inflammation  may  occur  at 
a  subsequent  date.  To  guard  against  this  possibility  ioni- 
zation of  the  root  canals  with  antiseptic  ions  is  an  effective 
method  of  treatment  in  those  cases.  Treatment  of  a  root 
canal  with  zinc  ions  in  the  manner  described  for  dead  teeth 
will  terminate  acute  periodontitis  much  quicker  than  by 
sealing  antiseptics  in  the  canal,  and  will  also  ensure  an 
aseptic  root,  which  can  be  filled  without  fear  of  recurrence 
of  the  trouble  at  a  subsequent  date. 

Silver  ions  obtained  from  a  weak  aqueous  solution  of 
silver  nitrate  are  also  effective  for  sterilizing  septic  roots 
of  this  kind,  but  on  account  of  the  staining  properties  of 
the  nitrate  of  silver  its  use  must  be  confined  to  back  teeth. 

The  most  favorable  cases  are  those  with  large  canals, 
which  admit  an  electrode  to  the  end  of  the  root.  Ions 
pass  readily  through  these  and  sterilize  the  tissues,  destroy- 
ing bacteria  which  have  infected  them  and  caused  the 
inflammation. 

A  case  of  the  brother  of  a  dentist  in  America  visiting 
this  country  is  typical  of  how  ions  act  on  periodontal  tissue. 
This  gentleman,  a  doctor,  two  years  ago  informed  me  that 
the  tooth  (a  lower  bicuspid)  had  a  temporary  filling  in  the 
root  which  could  be  easily  removed.  The  crown  cavity 
was  filled  with  cement  because  he  "so  often  had  to  have 
the  root  treated."  Periodontitis  was  very  acute  when  I 
saw  him  first.  Two  treatments  with  zinc  ions,  at  intervals 
of  two  days,  caused  a  permanent  cure  of  the  trouble.  The 
root  has-  now  been  filled  for  two  years  without  recurrence 
of  inflammation.  His  brother  wrote  me  for  information  of 
the  method  of  treatment,  saying  a  cure  had  been  effected 
is 


274  ELECTRO-THERAPEUTICS 

of  one  of  the  most  troublesome  cases  he  had  ever  had  to 
deal  with. 

Acute  Local  Periodontitis. — This  is  usually  caused  from 
toxic  products  of  bacteria  introduced  into  the  periodontal 
membrane  through  the  apical  foramens  of  the  root.  Clinic- 
ally the  condition  is  well  known,  and  need  not  be  described 
here.  If  the  abscess  has  not  assumed  large  dimensions 
and  some  of  the  pus  can  be  evacuated  by  way  of  the  pulp 
canal,  electrical  treatment  may  be  carried  out  as  follows: 
first  syringe  the  canals  to  remove  any  septic,  matter,  then 
wrap  a  fine  electrode  with  a  few  shreds  of  cotton  wool  and 
saturate  it  with  a  5  per  cent,  solution  of  zinc  chloride;  pass 
the  electrode  into  the  root  canal  as  far  as  it  will  go  and 
turn  on  5  ma.  current  for  8  minutes.  Zinc  ions  will  be 
introduced  into  the  abscess  area  sterilizing  it,  as  well  as  the 
septic  root  canal.  In  addition  to  this  the  inflamed  area 
of  tissues  over  the  root  of  the  tooth  should  be  treated  by 
applying  a  weak  aqueous  solution  of  tincture  of  iodine 
on  cotton  wool  and  pressing  it  into  position  with  a  flat 
platinum  electrode,  ionize  the  tissues  with  a  current  of 
3  or  4  ma.  for  five  minutes,  using  the  negative  pole. 

This  treatment  will  often  terminate  an  abscess  in  less  time 
than  the  ordinary  osmotic  method  of  sealing  antiseptics  in 
the  root  canal. 

Referring  to  this  method  of  treatment  of  the  surface 
area  over  the  root,  Dr.  J.  M.  Fogg,1  of  Philadelphia,  states 
that  the  current  has  been  to  him  of  greater  value  than  in 
any  other  class  of  cases.  He  advocates  the  cataphoric  use 
of  a  mixture  of  "saturated  solution  of  potassium  iodine, 
to  which  is  added  about  one-fifth  its  quantity  of  a  mix- 
ture of  equal  parts  of  tincture  of  iodine  and  aconite." 
And  he  states  that  "In  most  cases  one  application  is  all 
that  is  necessary  to  reduce  the  inflammation,  the  pain 
quickly  subsides,  and  there  is  seldom  a  recurrence  of  the 
disorder." 

By  this  method  of  mixing  drugs  which  are  both  electro- 

1  Dental  Cosmos,  vol.  xli,  p.  27. 


TREATMENT  OF  AVEOLAR  ABSCESS  275 

positive  and  electro-negative,  if  the  positive  pole  is  applied 
with  only  1  ma.  of  current  it  is  likely  that  no  cataphoric 
effects  take  place,  but  the  good  results  are  the  effects  of 
ionizing  the  tissues  with  potassium  and  aconite;  iodine  ions 
will  only  be  repelled  from  the  negative  pole. 

Perforation  of  the  Apex. — When  the  apex  has  been  per- 
forated by  a  drill,  septic  matter  may  readily  be  introduced 
into  the  periodontal  tissue  and  cause  inflammation,  if  not 
thoroughly  disinfected,  before  filling  the  root.  Perfect 
sterilization  can  be  insured  by  passing  an  electrode  to  the 
end  of  the  root  or  slightly  through  the  opening  and  ionizing 
the  tissues  with  an  antiseptic  salt,  such  as  3  per  cent,  zinc 
chloride,  or  copper  sulphate  2  per  cent.,  with  3  or  4  ma.  of 
current  for  a  few  minutes.    The  root  can  then  be  filled. 

Perforation  of  the  Side  of  the  Canal. — This  is  an  accident 
which  may  occur  in  crooked  or  constricted  roots,  and  is  a 
condition  which  is  regarded  by  many  as  hopeless.  J.  F. 
Colyer1  says:  "When  the  side  of  the  canal  has  been  per- 
forated there  is  but  slight  chance  of  saving  the  teeth." 
Until  the  author  tried  ionic  medication  in  these  cases  he 
found  great  difficulty  in  saving  these  teeth,  especially  if 
perforation  had  occurred  some  time  previously,  but  ioniza- 
tion of  the  perforation  and  the  whole  canal  has  proved 
to  him  that  perfect  sterilization  of  these  roots  and  proper 
subsequent  treatment  is  all  that  is  required  to  save  them. 
The  artificial  canal  should  be  ionized  with  zinc  ions,  intro- 
ducing a  dose  of  ions  into  the  tissues  through  the  aperture. 
The  perforation  should  then  be  plugged  with  a  lead  point 
on  the  principle  advocated  by  Dr.  J.  W.  Spaulding,2  of 
Paris. 

Alveolar  Abscess. — When  suppuration  has  occurred  and 
treatment  by  the  pulp  canal  is  impossible,  the  usual  course 
of  lancing  the  abscess  and  evacuating  the  pus  must  be 
resorted  to.  The  healing  of  the  abscess  can  be  greatly  facili- 
tated by  passing  a  zinc  or  copper  electrode  through  the 
opening  on  the  gums  and  ionizing  the  tissues  after  irrigating 

1  Dental  Surgery  and  Pathology,  p.  546. 

2  Dental  Cosmos. 


276  ELECTRO-THERAPEUTICS 

the  abscess  to  remove  the  pus.  These  soluble  electrodes 
repel  antiseptic  ions  into  the  affected  tissues  with  a  cur- 
rent of  3  or  4  ma.,  which  is  usually  readily  tolerated.  In 
addition,  as  soon  as  it  is  possible  to  treat  the  canal  of  the 
inflamed  tooth,  zinc  ions  from  a  solution  of  zinc  chloride 
should  be  introduced  into  the  interior  of  the  tooth.  This 
treatment  provides  a  thorough  method  of  sterilizing  the 
canal  and  may  prevent  subsequent  development  of  a 
fistulous  tract  leading  from  the  apex  of  the  root. 

In  cases  of  mandibular  teeth  affected  by  large  dento- 
alveolar  abscess  which  threatens  to  gravitate  to  the  outer 
surface  of  the  jaw,  ionic  medication  is  specially  indicated. 
It  furnishes  an  antiseptic  dressing  which  is  effective  and 
lasting.  In  these  cases  a  large  opening  into  the  abscess  is 
often  available  for  the  passing  of  a  good  sized  zinc  or  copper 
electrode.  This  should  be  covered  with  some  shreds  of 
cotton  wool  which  has  been  saturated  with  a  3  per  cent, 
solution  of  zinc  chloride,  or  2  per  cent,  copper  sulphate, 
and  a  current  of  3  to  4  ma.  passed  for  five  minutes.  Care 
should  be  taken  that  no  cotton  wool  is  left  in  the  wound. 

Chronic  Alveolar  Abscess. — Chronic  alveolar  abscess  in 
which  the  suppurative  process  has  extended  through  the 
alveolar  process  resulting  in  an  opening  on  the  gums  and 
the  formation  of  a  sinus  leading  to  the  apex  of  the  affected 
tooth.  This  condition  is  usually  caused  by  infection  of 
the  pulp  canal,  which  supplies  toxins  to  keep  up  a  sup- 
purative process.  When  this  condition  is  long-standing 
it  is  difficult  to  cure  by  the  ordinary  method  of  applying 
antiseptics  to  the  canal.  If  the  orifice  of  the  foramen  is 
not  artificially  sealed  it  is  often  an  easy  matter  to  cure 
these  cases  by  sterilizing  the  pulp  canal  with  zinc  ions, 
using  as  strong  a  current  as  possible  in  order  to  insure  a 
large  dose  of  ions  passing  through  the  apex;  the  canal  should 
then  be  temporarily  sealed,  a  copper  probe  should  be  passed 
into  the  sinus  through  the  external  opening  to  the  apex 
of  the  root,  where  it  should  be  left  in  situ,  and  to  it 
attached  the  anode,  a  current  of  3  to  5  ma.  should  then  be 
passed  for  about  five  minutes.    The  soluble  copper  electrode 


TREATMENT  OF  NECROSIS  277 

provides  copper  ions  which  permeate  the  fibrous  walls  of 
the  infected  tract,  sterilizing  it.  The  tissues  usually  ad- 
here firmly  to  the  copper  electrode,  and  may  be  loosened 
by  reversing  the  poles  for  a  short  time.  On  removal  it 
will  be  found  to  be  roughened  on  the  surface  and  reduced 
in  size;  a  green  stain  will  also  be  seen  in  the  tissues.  These 
ions  are  of  highly  antiseptic  quality,  and  often  a  single 
treatment  will  cure  a  chronic  abscess,  but  two  or  three 
treatments  may  be  necessary. 

If  the  sinus  extends  to  the  skin  on  the  outside  of  the 
face,  and  it  is  desired  to  save  the  tooth,  the  pulp  canal 
should  be  sterilized  as  before  with  zinc  ions,  and  the  sinus 
probed  as  described,  and  disinfected  with  copper  ions  in- 
troduced into  it.  These  cases  may  be  accompanied  by 
cicatricial  adhesion  of  the  sinus  by  a  fibrous  cord  to  the 
surface  of  the  bone,  which  results  in  an .  ugly  scar.  For 
this  condition  chlorine  ions  introduced  into  the  scar  tissue 
has  been  advocated  by  some  authors  to  soften  and  dispel 
the  cicatrix  (see  British  Medical  Journal,  August  31,  1912). 

Necrosis  of  the  Jaws. — Necrosis  of  the  jaws  is  often  con- 
fined to  the  alveolar  process.  In  private  practice  this  is 
the  form  most  often  seen,  and  is  generally  caused  by  septic 
infection  following  traumatism,  arsenious  acid  poisoning, 
or  chronic  septic  infection  of  the  apices  of  teeth.  In  these 
cases  the  sequestrum  should  be  removed,  if  separated,  or 
the  surface  of  the  necrosed  bone  burred  away  and  the 
debris  syringed  out,  after  this  a  platinum  electrode  in- 
troduced to  the  affected  area  with  a  solution  of  tincture 
of  iodine  diluted  with  equal  parts  of  water  and  a  current 
of  5  ma.  or  more,  if  not  painful,  passed  from  a  cathode, 
the  liquid  solution  can  be  conveyed  on  cotton  wool  wound 
about  the  electrode.  Should  considerable  pus  be  present, 
zinc  chloride  3  per  cent,  solution  should  be  used  at  the 
first  treatment  with  the  anode,  and  iodine  subsequently 
with  the  cathode. 

Copper  ions  from  a  soluble  copper  electrode  are  also 
useful,  but  iodine  ions  seem  to  be  the  ion  indicated  for  these 
cases. 


278  ELECTRO-THERAPEUTICS 

In  chemical  poisoning  cases  from  arsenious  acid,  which 
has  leaked  out  of  a  cavity  and  affected  the  gums  and  border 
of  the  alveolus,  if  the  affected  area  is  freely  cut  with  a  sharp 
burr  and  syringed  with  warm  water,  then  a  platinum 
electrode,  wound  with  cotton  wool  and  saturated  with  a 
weak  solution  of  tincture  of  iodine  and  water,  applied  with 
the  negative  pole,  using  1  or  2  ma.  for  a  few  minutes,  the 
necrosis  will  be  arrested  often  after  a  single  treatment. 

More  extensive  necrosis  of  the  alveolus  can  be  treated  in 
this  manner  with  zinc  and  iodine  ions  to  terminate  the  dis- 
ease in  a  remarkably  short  time  in  comparison  to  ordinary 
irrigation  methods. 

A  case  to  illustrate  this  may  be  mentioned.  A  lady  was 
sent  to  me  by  a  throat  specialist  about  two  years  ago  with 
necrosis  of  the  alveolus  extending  from  the  first  bicuspid  to 
the  first  molar  in  the  maxilla  on  the  left  side.  The  first 
bicuspid  had  been  extracted  and  a  hollow  drainage  tube 
inserted  into  the  socket,  supported  in  position  by  a  small 
gold  plate.  She  had  worn  this  plate  for  many  months, 
and  was  quite  expert  in  syringing  out  the  affected  tract, 
which  she  did  many  times  a  day.  She  was  certain  that 
she  could  not  do  without  the  drainage  tube  for  twenty-four 
hours  as  "the  pain  would  be  intense,"  and  nearly  refused 
further  treatment  when  I  refused  to  allow  her  to  replace 
it  after  the  first  treatment.  The  area  of  exposed  bone  was 
narrow  and  about  one  inch  long.  Zinc  ions  were  intro- 
duced with  about  4  ma.  current  daily  for  a  week,  at  the 
end  of  which  time  no  pus  was  present  and  the  tract  was 
nearly  closed;  in  a  fortnight  from  the  first  treatment  the 
opening  healed  completely.  The  patient's  general  health 
was  exceedingly  bad,  and  she  has  recently  become  bed- 
ridden with  rheumatoid  arthritis. 

The  author  has  not  tried  the  effect  of  ions  in  cases  of 
extensive  necrosis  of  the  jaws  resulting  from  exanthematous 
fevers,  phosphorus,  mercury,  or  extensive  trauma,  but 
bacteria  infection  is  always  present  in  these  cases,  and  it 
is  a  question  whether  surgical  and  other  treatment  would 


TREATMENT  OF  MARGINAL  GINGIVITIS  '      279 

not  be  greatly  aided  by  the  introduction  of  antiseptic  ions 
into  the  affected  area. 

Marginal  Gingivitis. — A  form  of  gingivitis  is  sometimes 
met  with  which  is  exceedingly  painful  and  difficult  to  deal 
with;  the  gingival  border  is  red  and  inflamed  around  the 
necks  of  the  teeth,  principally  on  the  external  surfaces  for 
a  limited  space,  but  uniformly  about  the  entire  denture, 
the  papilla-like  portion  of  the  gums  between  the  teeth  break 
down  and  slough  on  the  surface,  but  there  is  little  or  no 
hypertrophy  nor  is  the  inflammation  of  a  proliferative 
character.  The  condition  is  found  in  adults,  and  is  some- 
times associated  with  digestive  disturbances  due  sometimes 
to  high  living  and  the  free  use  of  wines.  The  condition 
resembles  the  acutely  painful  condition  of  the  gums  in 
ordinary  stomatitis  without  the  general  congestion  of  the 
mucous  membrane,  etc.  The  patient  complains  of  constant 
pain  in  the  gums,  which  is  increased  by  taking  solid  food. 

In  these  cases  the  author  has  found  the  application  of 
10  per  cent,  solution  of  argyrol  to  the  gums  with  a  low 
current  of  0.5  to  1  ma.  to  be  a  soothing  dressing  for  the  first 
treatment.  Argyrol  is  a  colloid  substance  (a  silver  prepa- 
ration made  with  nucleinic  acid)  which  is  not  supposed 
to  ionize,  but  the  current  may  have  the  effect  which  is 
undoubtedly  beneficial.  The  application  should  be  made 
by  saturating  cotton  wool  with  the  solution  and  placing 
it  about  the  necks  of  the  teeth,  covering  three  or  four  at  a 
time  and  applying  a  platinum  anode  laid  flat  over  the  sur- 
face. Subsequent  treatment  should  consist  in  applying  a 
weak  solution  of  tincture  of  iodine  in  water  in  the  same 
manner,  using  the  cathode  and  2  or  3  ma.  current  for  a  few 
minutes  to  each  application.  This  relieves  the  pain  in  a 
short  time  and  a  few  treatments  usually  cure  the  con- 
dition. Local  treatment  such  as  cleansing  the  teeth  and  a 
proper  mouth  wash  and  attention  to  diet  are  also  necessary. 


CHAPTER  XIV. 
TREATMENT  OF  PYORRHCEA  ALVEOLARIS. 

Periodontal  Disease — Incipient  Infection  of  the  Gingival  Trough — 
Septic  Infection  of  Gingival  Trough  without  Suppuration — Septic  Infection 
of  Periodontal  Membrane — Acute  Septic  Infection  of  Gums  and  Perio- 
dontal Membrane — Chronic  Septic  Periodontitis. 

Periodontal  Disease. — This  includes  a  variety  of  acute  and 
chronic  forms  of  periodontal  affections  which  are  not  pyor- 
rhoea alveolaris  in  the  incipient  stages,  but  which  invariably 
lead  to  suppuration  of  the  periodontal  area,  when  it  is  cor- 
rectly termed  pyorrhea  alveolaris.  But  terms  and  descrip- 
tions of  the  disease,  etiology,  bacteriology,  and  pathology 
are  not  the  phases  of  the  disease  with  which  this  work  is 
intended  to  deal;  it  is  treatment  which  will  be  chronicled 
from  an  electrical  standpoint. 

It  will  be  necessary  to  describe  different  stages  of  the 
disease,  for  which  different  kinds  of  treatment  are  necessary. 

The  author  must  here  emphasize  one  point  which  is  not 
to  be  overlooked  in  respect  to  treatment,  if  any  good  re- 
sults are  to  be  obtained  from  electrical  treatment  of  any 
of  the  phases  of  periodontal  disease.  This  point  will  be 
understood  as  having  been  carried  out,  in  referring  to  the 
treatment  of  the  disease,  and  will  not  be  again  mentioned. 
It  is,  unless  all  the  calcareous  deposits  or  any  form  of  foreign 
matter  found  on  teeth  affected  in  any  way  by  periodontal 
disorders  is  completely  removed,  and  the  surface  of  the  teeth 
to  which  this  foreign  matter  adheres  thoroughly  polished, 
no  good  results  will  be  obtained.  It  is  absolutely  a  waste  of 
time  to  attempt  ionic  treatment  of  pyorrhoea  alveolaris  if 
any  particles  of  calcareous  deposit  are  left  clinging  to  the 
roots  of  the  teeth.  Indeed,  the  surest  guide  to  the  non- 
fulfilment  of  this  condition  in  the  treatment  is  to  see  the 


TREATMENT  OF  PYORRHCEA  ALVEOLARIS        281 

whole  denture  become  perfectly  normal  and  the  disease 
cured,  except  here  and  there  a  tooth  in  which  this  condition 
has  not  been  fulfilled.  It  is  a  difficult  matter,  but  it  is 
nearly  always  possible  to  remove  salivary  calculus  from 
the  roots  of  the  teeth  affected  by  periodontal  disease  of 
the  chronic  type.  It  may  require  hours  of  hard  work  to 
accomplish  this,  but  it  should  be  done,  not  necessarily  at 
two  or  three  sittings,  but  extended  over  the  whole  course 
of  the  treatment,  if  that  should  take  weeks  or  even  months. 
A  great  many  dentists  pass  through  a  long  life  of  practice 
without  ever  mastering  the  details  of  scaling  tartar,  this 
failure  of  one  of  the  first  principles  in  the  treatment  of 
periodontal  disease  spells  failure  altogether  in  the  attempts 
made  to  cure  the  disease  by  application  of  drugs.  Some 
are  content  to  slur  over  this  dogmatic  rule  and  satisfy  their 
vanity  with  thoughts  of  "constitutional  causes,"  and  to 
term  such  a  rule  a  "tartar  bogey."  These  gentlemen  never 
mire  pyorrhoea  alveolaris. 

For  convenience  of  description  the  different  phases  of 
periodontal  disease  are  here  classified  as  follows: 

1.  Incipient  infection  of  the  gingival  "trough"  or  space. 

2.  Septic  infection  of  the  gingival  trough  without  suppu- 
ration 

3.  Chronic  septic  infection  of  the  periodontal  membrane 
without  visible  suppuration,  "dry  pyorrhoea." 

4.  Acute  septic  infection  of  gums  and  periodontal  mem- 
brane without  visible  pus. 

5.  Chronic  septic  periodontal  disease  with  pus. 

1.  Treatment  of  Incipient  Infection  of  the  Gin- 
gival Trough. — Reference  is  here  made  to  the  gingival 
trough  or  space  because  it  is  the  starting-point  of  general 
chronic  alveolar  pyorrhoea.  This  space  is  a  natural  one 
formed  by  the  gingival  margin  and  the  surface  of  the  tooth. 
In  a  very  large  percentage  of  healthy  mouths,  if  this  space 
be  examined,  it  will  be  found  to  contain  some  form  of 
foreign  matter;  rarely,  if  ever,  is  it  perfectly  free  from 
deposits  of  salivary  calculus  or  food  in  a  state  of  stagnation 
or  decomposition. 


282 


ELECTRO-THERAPEUTICS 


If  a  flat  platinum  probe  be  passed  into  the  gingival 
space  parallel  with  the  long  axis  of  the  teeth  and  moved 
around  on  the  contour  of  the  necks  of  the  teeth,  it  will  be 
found  that  in  almost  every  adult  an  irregularity  of  surface 
or  roughness  can  be  detected  by  the  sense  of  touch  as  the 
probe  passes  over  the  surfaces,  if  not  in  all  the  teeth  nearly 
constantly  is  this  the  case  about  the  mandibular  incisor 
and  maxillary  molars  on  the  buccal  aspect.  The  gingival 
trough  is  always  infected  by  bacteria  of  the  oral  cavity,  and 
it  is  impossible  to  demark  at  what  stage  in  subsequent 
irritation  of  the  gingival  margin  (which  is  inevitable  when 

Fig.   142 


A,  gingival  trough;  B,  alveolus;  C,  periodonta   membrane. 


foreign  substances  are  present)  inflammation  really  begins, 
in  order  to  prevent  the  development  of  periodontal  disease. 
It  is  advisable  to  cleanse  the  gingival  trough  by  removing 
salivary  calculus  or  stagnant  food  and  polish  the  tooth 
surface  which  forms  one  of  its  boundaries;  a  platinum 
electrode  should  then  be  wound  with  a  little  cotton  wool 
and  saturated  with  a  weak  aqueous  solution  of  iodine  and 
passed  into  the  spaces  from  which  any  foreign  substance 
has  been  removed;  a  current  of  2  or  3  ma.  from  the  negative 
pole  applied  by  slowly  moving  the  electrode  for  a  few 
minutes  about  the  spaces  under  treatment,  will  ionize  the 
tissues  with  iodine  ions  and  sterilize  the  parts,  which  may 


TREATMENT  OF  PYORRHCEA  ALV SOLARIS        283 

be  in  the  incipient  stages  of  infection  with  pus-producing 
varieties  of  micro-organisms.  The  gum  margins  treated  in 
this  manner  assume  a  tough,  healthy  appearance  which 
will  remain  so  until  it  again  becomes  irritated  by  stagnant 
food  or  fresh  deposits  of  calcareous  salts.  This  may  take 
years,  or  may  occur  much  sooner,  and  should  be  treated 
whenever  foreign  substances  are  detected,  as  by  this  means 
definite  unmistakable  septic  infection  of  the  gums  and  perio- 
dontal membrane  can  be  averted. 

Mr.  Hopewell  Smith,  in  referring  to  the  "  Normal  arrange- 
ment of  the  osseous  and  fibrous  tissues"  (see  Dental  Cosmos, 
vol.  liii,  p.  981),  says:  "It  is  the  writer's  belief  that  not  only 
do  all  human  teeth  possess  spaces  around  their  necks,  which 
may  become  potential  cavities  for  the  retention  of  micro- 
organisms, but  that  if  great  care  be  exercised  in  the  labora- 
tory manipulations;  it  will  be  found  that  micro-organisms 
can  always  be  demonstrated,  in  ordinary  circumstances, 
occupying  the  site  thus  produced.  It  is  when  they  are  of 
the  pus-producing  varieties  that  pyorrhoea  alveolaris  is 
established."  This  being  the  case,  as  undoubtedly  it  is, 
the  method  of  eradicating  these  micro-organisms  referred 
to  must  effectively  prevent  the  beginning  of  pyorrhoea 
alveolaris.  There  can  be  little  doubt  that  antiseptic  ions 
introduced  electrically  into  tissues  have  the  effect  of  destroy- 
ing micro-organisms. 

2.  Septic  Infection  of  the  Gingival  Trough  with- 
out Suppuration. — This  is  the  second  stage  of  local 
septic  periodontal  disease,  in  which  inflammation  of  the 
gum  tissue  is  discernible.  The  gingival  trough  in  these 
cases  is  found  to  contain  salivary  calculus  often  extending 
from  the  enamel  surfaces  of  the  teeth  which  have  been 
badly  kept;  but  it  is  just  as  often  found  (in  teeth  which 
have  been  well  kept  and  regularly  attended)  to  contain 
nodules  of  hard  dark  calculus,  which  is  most  tenacious  and 
difficult  to  remove.  Inflammation  has  been  caused  by  the 
presence  of  the  foreign  substance  in  contact  with  the  deli- 
cate epithelial  lining  of  the  gingival  fold,  and  the  invasion 
of  bacteria.    Often  the  deposit  is  rough  and  sharp,  causing 


284  ELECTRO-THERAPEUTICS 

bleeding  of  the  gums  on  the  slightest  pressure  The  ionic 
treatment  indicated  consists  in  passing  zinc  ions  from  a 
3  per  cent,  aqueous  solution  with  a  zinc  electrode  into  the 
space  of  inflamed  area  with  a  current  of  2  or  3  ma.  from  the 
-j-  pole  for  the  first  treatment,  and  if  subsequent  treat- 
ment is  necessary,  iodine  ions  from  the  —  pole.  These 
cases  yield  immediately  to  treatment  with  ions  and  the 
tissues  return  to  normal  condition,  if  allowed  to  relapse  into 
frequent  recurrences  eventually  recession  of  the  gums  and 
exposure  of  the  necks  of  the  teeth  is  the  result 

This  stage  of  periodontal  disease  is  often  regarded  as  a 
simple  inflammatory  condition  of  the  gums  having  little 
bearing  on  pyorrhoea  alveolaris;  whereas  it  should  be  looked 
upon  as  a  most  serious  symptom  of  pyorrhoea  alveolaris.  It 
is  that  stagnation  stage  insisted  upon  by  Mr.  J.  G.  Turner 
in  which  he  recognizes  the  beginning  of  pyorrhoea. 

At  this  stage  infection  of  the  gums  by  pyogenic  bacteria 
has  already  taken  place,  and  although  the  ordinary  method 
of  cleansing  the  teeth  and  prescribing  antiseptic  washes 
seems  to  restore  the  tissues  to  the  normal  condition,  it 
cannot  eradicate  the  bacteria  as  effectively  as  the  passing 
of  antiseptic  ions  into  the  tissues,  besides,  the  stimulating 
effect  of  the  current  on  the  tissues  is  valuable  for  increasing 
local  metabolism  and  elimination  in  a  congested  area,  and 
a  most  lasting  effect  is  obtained  by  ionic  treatment. 

The  author  is  convinced  of  the  local  nature  of  pyorrhoea. 
It  always  starts  with  a  local  stagnation  area  of  the  gums 
at  the  gingival  trough,  associated  with  septic  infection  of 
the  tissues.  If  general  disease  of  the  body  has  any  influ- 
ence it  is  because  local  cleanliness  is  neglected  or  impossible 
during  illness,  and  infection  is  established  from  oral  sepsis. 

That  there  is  ever  a  gouty  diathesis  associated  with  uric 
acid  which  can  be  termed  peculiar  to  a  certain  form  of  pyor- 
rhoea is  open  to  question.  The  only  peculiarity  which 
manifests  itself  in  these  so-called  "gouty  periodontitis" 
cases,  is  the  excess  of  local  irritant  in  the  form  of  salivary 
calculus,  which  if  recognized  in  proper  time  and  kept 
from   producing    stagnation    and    septic    infection    of    the 


TREATMENT  OF  PYOBRHCEA  ALVEOLARIS        285 

tissues,  will  produce  no  specific  form  of  pyorrhoea.  There 
seems  to  be  no  more  difficulty  in  treating  periodontitis  in 
cases  of  recognized  general  gouty  diathesis,  by  ionic  medi- 
cation, than  any  other  ordinary  inflammatory  condition 
of  the  muco-periodontal  membrane.  The  chief  difficulty 
appears  to  be  the  recognizing  of  the  early  stages  of  the 
disease,  when  it  is  readily  cured. 

3.  Septic  Infection  of  the  Border  of  the  Perio- 
dontal Membrane  without  Visible  Suppuration. 
"Dry  Pyorrhcea.'  — This  phase  of  periodontal  disease 
is  most  subtle  and  is  rarely  recognized  in  the  incipient 
stages.  It  follows  the  second  stage  already  described.  The 
irritation  set  up  in  the  gums  by  the  presence  of  foreign 
substances  and  bacterial  infection  extends  to  the  dental 
ligament  by  a  slow  process  which  is  nevertheless  sure,  and 
it  passes  deep  into  the  periodontal  membrane  before  the 
necks  of  the  teeth  become  exposed  and  the  gum  thinned 
to  a  mere  layer  of  mucous  membrane  which  clings  closely 
to  the  necks  of  the  teeth,  the  interdental  papilla  dis- 
appears and  the  margin  of  the  alveolus  becomes  absorbed; 
the  teeth  are  quite  firm.  It  occurs  in  well-kept  mouths  and 
is  often  attributed  by  dentists  to  over-brushing.  It  is  often 
associated  with  gouty  or  rheumatic  diathesis,  and  termed 
by  some  authors  gouty  periodontitis,  which  is  rarely  recog- 
nized before  the  age  of  thirty.  The  author  considers  this 
"gouty  diathesis"  to  be  a  coincidence  which  has  little  to 
do  with  the  direct  cause  and  progress  of  this  disease,  except 
for  the  furnishing  of  an  irritant  in  the  form  of  minute 
granular  deposits  of  hard  calculus  which  adheres  firmly 
to  the  roots  of  the  teeth,  and  in  the  first  instance  starts  the 
inflammatory  action  and  the  attendant  bacterial  infection 
of  a  subtle  and  slowly  progressive  character.  A  flat  probe 
pressed  between  the  thin,  taut  layer  of  tissue  and  the  roots 
of  the  teeth,  will  reveal  considerable  loss  of  periodontal 
attachment  and  always  a  layer  of  calcareous  deposit, 
sometimes  in  dark,  hard  nodules,  but  more  often  of  a  finely 
granular  nature,  most  difficult  to  detect.  This  form  of 
periodontal  disease  is  most  difficult  to  deal  with.    If  recog- 


286  ELECTRO-THERAPEUTICS 

nized  in  the  early  stages  the  gums  are  not  wasted,  and  the 
removal  of  calculus  is  not  as  difficult  as  later  when  a  thin 
stretched  layer  of  mucous  tissue  resists  the  proper  use  of 
scalers  and  the  polishing  process.  Treatment  consists  in 
removing  the  irritant  and  sterilization  of  the  infected  gums 
and  periodontal  tissues.  This  latter  can  be  accomplished 
by  passing  a  thin  platinum  electrode  into  the  spaces,  carry- 
ing a  shred  of  cotton  wool  saturated  with  a  3  per  cent, 
solution  of  zinc  chloride,  with  a  current  of  2  to  4  ma.  ac- 
cording to  the  ability  of  the  patient  to  stand  the  current. 
The  electrode  must  be  moved  around  the  necks  of  the  teeth 
to  insure  every  part  of  the  affected  area  being  saturated 
with  zinc  ions.  The  necks  of  the  teeth  are  sometimes 
exceedingly  sensitive  in  these  cases,  and  0.5  to  1  ma.  cur- 
rent will  be  all  that  is  possible  to  use,  but  even  this  low  cur- 
rent strength  seems  sufficient  to  arrest  the  progress  of  the 
disease  and  to  improve  the  sensitive  nature  of  the  cementum. 
One  case  of  many  the  author  has  successfully  treated  may 
be  mentioned.  Lady  R.  five  years  ago  consulted  me  for 
"receding  gums."  The  necks  of  the  maxillary  incisors 
and  cuspids  were  exposed  and  the  premolars  and  molars 
were  showing  signs  of  the  trouble;  the  teeth  were  highly 
sensitive  to  thermal  changes  and  also  to  electric  current. 
Salivary  calculus  of  a  hard,  dark,  granular  type  was  found 
beneath  the  gum  margin  on  every  tooth,  and  principally 
in  the  interspaces,  the  dental  papilla  had  disappeared 
from  the  spaces  of  the  superior  incisors.  The  teeth  were 
absolutely  free  from  caries  and  were  beautifully  white,  even, 
and  well  kept.  She  informed  me  that  her  dentist  had 
cleaned  them  four  times  a  year.  The  periodontal  membrane 
and  gums  were  treated  with  zinc  ions  and  iodine  ions. 
At  the  first  course  of  treatment,  which  extended  over  six 
weeks,  the  current  of  0.5  to  1  ma.  was  all  that  could  be  used 
on  the  anterior  teeth  on  account  of  extreme  sensitiveness 
of  the  necks  of  the  teeth.  The  treatment  was  renewed 
at  intervals  of  four  months  for  a  year  and  the  gingival 
trough  examined  for  deposits.  After  the  first  year  the 
patient  was  seen  once  every  six  months  and  one  treatment 


TREATMENT  OF  PYORRHCEA  ALVEOLARIS        287 

given.  The  sensitiveness  of  the  dentine  has  gradually 
disappeared,  and  at  a  recent  sitting  I  passed  a  current  of 
4  ma.  about  the  necks  of  the  superior  incisors  without  pain. 
These  teeth  five  years  previously  were  painful  to  0.5  ma. 
current  strength.  The  "dry  pyorrhoea"  has  progressed  no 
further,  and  the  course  of  the  disease  has  undoubtedly  been 
checked.  This  is  a  typical  case  of  many  treated  similarly 
with  zinc  and  iodine  ions  which  have  been  successful. 

Fetid  odor  is  often  complained  of  by  patients  affected 
with  this  form  of  periodontal  disease,  and  is  sometimes 
the  only  discomfort.  This  will  disappear  entirely  under 
zinc  ionization  and  will  be  the  first  indication  to  the  patient 
that  improvement  is  in  progress.  The  fetor  is  usually  due 
to  bacterial  infection  of  the  interspaces  of  molars  which 
may  show  no  signs  of  disease  on  the  buccal  aspects  of  well 
kept  teeth. 

4.  Acute  Septic  Infection  of  Gums  and  Periodontal 
Membrane;  Inflammation  without  Visible  Pus. — 
This  stage  of  the  disease  is  marked  by  congestion  of  the 
gums,  the  papilla  are  enlarged  and  heaped  up  between 
the  teeth  in  loose  tags  which  bleed  freely  when  touched, 
the  gingival  trough  is  greatly  deepened  by  the  loss  of  the 
dental  ligament  and  contains  nodules  of  calculus;  inflam- 
mation of  the  gum  margin  is  general,  and  the  operation  of 
scaling  is  attended  with  copious  bleeding.  This  may  be 
the  condition  extending  to  the  entire  denture  without 
any  deep  pockets  being  present,  or  may  be  the  condition 
only  of  a  certain  area,  other  parts  of  the  mouth  being 
only  slightly  affected,  or  may  be  the  area  leading  up  to 
a  much  worse  area  of  infection,  which  has  succumbed  to 
the  ravages  of  acute  pyorrhoea  alveolaris.  The  clinical 
appearance  varies  considerably,  but  is  that  stage  which 
is  marked  by  considerable  inflammation  without  the  break- 
ing down  of  the  tissues  into  visible  pus  exuding  from  the 
interspaces. 

Treatment  at  first  is  painful  if  high  currents  are  passed; 
10  per  cent,  argyrol,  from  which  silver  ions  are  obtained, 
passed  with    a   current   of   1    or   2   ma.,  act  as  a  soothing 


ELECTRO-THERAPEUTICS 

dressing,  and  subsequent  treatment  with  zinc  ions  passed 
into  the  gums  and  periodontal  membrane  with  a  current 
of  2  to  5  ma.  will  arrest  the  progress  of  inflammation.  If 
the  calculus  is  completely  removed  and  the  surfaces  ren- 
dered smooth  this  stage  of  the  disease  may  be  checked 
by  the  complete  sterilization  of  the  affected  parts,  the 
gums  become  tough  and  return  to  their  normal  position 
about  the  teeth.  Reinfection  will  depend  on  the  patient's 
ability  to  keep  the  teeth  free  from  accumulation  of  foreign 
matter,  which  they  are  often  able  to  do  with  periodical 
assistance  of  their  dentist  and  further  treatment  in  case 
inflammation   is   present. 

With  respect  to  the  use  of  argyrol  and  nargol  with  the 
electric  current  it  is  uncertain  what  action  takes  place. 
Argyrol  is  a  compound  preparation  of  silver  with  nucleinic 
acid  which  is  classed  electrically  under  the  heading  of 
colloid  preparations,  which  are  not  acted  upon  to  form 
ions.  Clinically  argyrol  with  a  weak  current  seems  to 
impart  a  soothing  effect  on  lacerated  gum  tissues,  and  it 
is  possible  the  preparation  has  the  same  effect  without 
the  current,  but  that  when  used  electrically  the  effect  is 
beneficial. 

5.  Chronic  Septic  Periodontitis  with  Pus. — This 
stage  of  the  disease  is  a  progressive  inflammatory  con- 
dition of  the  periodontal  membrane  involving  the  alveolar 
process  which  becomes  absorbed  in  the  presence  of  pus 
and  micro-organisms,  forming  spaces  about  the  sockets  of 
the  teeth  into  which  pus  collects.  It  may  occur  in  only 
one  or  two  teeth  (see  :r-ray,  Fig.  143)  as  the  starting-point 
of  a  general  merging  from  a  less  advanced  stage  of  perio- 
dontal disease  into  this  suppurative  condition.  It  is  un- 
necessary to  dilate  on  the  general  symptoms  of  pyorrhoea 
alveolaris,  they  are  well  known  to  all.  It  is  unfortunate 
when  it  is  not  recognized  in  the  earlier  stages  and  treated, 
for  then  it  is  readily  cured. 

Electrical  treatment  in  acute  cases  of  pyorrhoea  alveo- 
laris is  undoubtedly  a  great  help  in  combating  the  disease. 
The  suppuration  can  always  be  checked  by  ionic  steriliza- 


TREATMENT  OF  PYORRHCEA   A LV SOLARIS 


289 


tion,  provided  the  many  causes  of  a  mechanical  or  irritat- 
ing nature  are  recognized  and  removed.  The  writer  is  of 
the  opinion  that  predisposing  and  constitutional  compli- 
cations are  more  often  an  effect  than  a  cause,  and  they 
disappear  after  the  disease  has  been  cured. 

Fig.   143 


The  treatment  consists  of  carrying  out  the  conditions  re- 
ferred to  in  respect  to  the  removing  of  calculus  (see  p.  280). 
During  this  long  and  tedious  process  the  pockets  should 
be  sterilized  by  passing  a  zinc  electrode  wound  with  cotton 
wool  carrying  3  per  cent,  solution  of  zinc  chloride  into 
them,  the  electrode  should  be  kept  steady  in  one  position 
while  the  current  is  being  turned  on;  in  this  way  it  is  often 
possible  to  use  a  larger  current  strength,  5  ma.  should  be 
the  amount  aimed  at;  in  the  interspaces  of  molars  it  is 
sometimes  possible  to  use  10  to  15  ma.  The  stronger  the 
current  the  deeper  will  be  the  penetration  of  ions,  and  the 
more  perfect  the  sterilizing  effect.  The  electrode  should  be 
kept  in  position  for  a  minute  or  two  at  a  time  and  moved 
to  an  adjoining  part  of  the  affected  area  for  the  same  space 
of  time,  returning  to  the  original  spot  after  medicating 
other  parts;  this  makes  the  operation  less  irksome  to  patient 
and  operator.  The  dose  of  ions  will  depend  on  the  strength 
of  current  which  can  be  used.  If  the  teeth  are  sensitive 
or  the  patient  a  bad  subject  for  electrical  treatment,  the 
19 


290 


ELECTRO-THERAPEUTICS 


ionic  effect  will  be  less  marked,  and  recovery  slower.  The 
active  electrode  should  be  as  large  as  possible,  and  curved 
to  the  contour  of  the  roots  of  the  teeth,  but  not  be  pointed, 
as  it  must  be  remembered  that  the  density  of  the  current 
is  greatest  at  the  point.  Every  precaution  should  be  taken 
to  prevent  undue  pain  or  shocks  from  the  current,  at  the 
same  time  it  is  desirable  to  get  the  effect  of  as  large  a  cur- 
rent as  possible;  5  ma.  is  usually  sufficient,  but  if  a  stronger 
current  can  be  used  it  is  more  effective.  The  electrode 
should  reach  the  bottom  of  each  pocket. 

Fig.   144 


X-ray  of  a  case  under  treatment. 


The  patient's  cooperation  and  assistance  is  necessary 
during  and  after  treatment.  To  obtain  this  no  small  amount 
of  pain  is  necessary  to  teach  a  useful  hygienic  method, 
which  should  consist  in  brushing  with  a  stiff  brush,  first 
with  a  powder,  and  then  with  an  alcoholic  antiseptic  solution 
which  should  be  dropped  on  a  wet  brush,  such  as : 

3 — Thymol gr.  iij 

Benzoic  acid      ...  5ss 

01.  cinnam Tfl,x 

Acid,  carbolic TUxxx 

Otto  rosse TTlxv 

Alcohol ad  giv — M. 

and  the  interspaces  of  all  teeth  should  be  cleansed  daily  by 
passing  waxed  floss  silk  between  the  teeth. 


TREATMENT  OF  PYORRHEA  ALVEOLARIS        291 

The  clinical  aspect  of  the  alveolus  before  and  after  treat- 
ment must  now  be  referred  to.  The  passing  of  a  current 
of  even  a  few  milliamperes  into  tissues  by  a  conductor 
electrode  of  such  small  area  and  cross-section  as  one  which 
will  pass  into  an  ordinary  pyorrhoea  pocket,  intensifies 
the  density  at  the  contact  of  the  electrode  to  an  extent 
that  amplifies  the  action  of  the  current  at  that  point  to  a 
degree  far  in  excess  of  the  action  of  large  electrodes  used 
in  medical  practice  for  ionization  of  large  surfaces;  for 
example,  in  the  application  of  quinine  or  salicylic  ions  for 
treatment  of  trigeminal  neuralgia  the  area  of  the  electrode 
extends  over  the  entire  surface,  and  20  to  30  ma.  current 
is  required  to  pass  ions  successfully  to  the  affected  nerves. 
In  comparison,  an  electrode  passed  into  periodontal  tissue 
is  of  an  area  of  2  x  1  mm.  and  1  cm.  long  with  a  current  of 
5  ma.  it  conveys  a  concentration  or  density  of  current 
many  hundred  times  greater  than  the  large  flat  electrode. 
It  is  impossible  to  say  to  what  depth  ions  penetrate  into 
the  alveolus  by  this  treatment.  The  stimulating  effect  of 
the  current  must  also  be  great.  These  considerations 
must  weigh  heavily  in  the  actual  clinical  changes  to  be 
noted  after  ionic  treatment  of  pyorrhoea  alveolaris.  Mr. 
Hopewell  Smith,1  in  his  concluding  notes  on  "Patho- 
histology"  of  pyorrhoea  alveolaris,  referring  to  the  treatment 
of  the  disease  says:  "The  hopelessness  of  retaining  the  teeth 
and  of  building  up  bone  which  has  been  lost  by  absorption 
or  the  recalcification  of  decalcified  foundations  must  be 
apparent."  "The  treatment,  at  best,  can  only  be  palliative 
and,  unfortunately,  only  directed  to  a  prevention  of  further 
distinction,  and  not  the  rehabilitation  or  reconstruction 
of  parts  absolutely  forever  destroyed."  The  writer  is  not 
so  sure  that  these  conclusions  about  recalcification  of 
decalcified  foundations  are  correct;  at  any  rate,  they  are 
open  to  question.  It  is  not  useless  or  hopeless  to  retain 
a  set  of  teeth  which  is  badly  affected  by  pyorrhoea  in 
functional  usefulness,  without  septic  infection  for  a  space  of 

1  Dental  Cosmos,  vol.  liii,  p.  991. 


292 


ELECTRO-THERAPEUTICS 


fourteen  years,  or  even  for  six  years,  even  if  it  is  necessary 
to  treat  the  teeth  twice  a  year  in  order  to  attain  such  results. 
Nor  is  it  impossible  for  the  alveolus  to  reform  about  the 
sockets  of  the  teeth  affected  by  pyorrhoea.  The  case  C, 
reported  on  p.  249,  is  one  in  which  extensive  pyorrhoea 
with  constitutional  symptoms  accompanying  it  existed, 
the  pockets  on  the  palatal  aspect  of  the  incisors  extended 
to  nearly  the  apices,  every  symptom  of  chronic  pyorrhoea 

Fig.  145 


Case  C,  Model  1  before  treatment,  and  2  fourteen  years  later. 


existed.  When  the  teeth  were  retracted  to  the  position 
of  the  diagram  on  p.  150  they  were  so  loose  that  they  could 
be  moved  forward  a  distance  of  about  5  mm.  without 
touching  a  bony  socket.  The  bone  has  reformed  in  those 
empty  sockets,  and  not  only  reformed  but  grown  thicker  on 
the  labial  aspect  of  the  alveolus  than  is  normal,  as  shown 
by  the  photograph  of  the  models  taken  before  treatment 
and  fourteen  years  later.     The  recurrence  of  pyorrhea  has 


TREATMENT  OF  PYORRHCEA  ALVEOLARIS 


293 


not  taken  place  in  the  time  stated,  no  teeth  have  been  lost 
and  the  once  diseased  denture  has  been  functional  for  years 
without  retrograde. 

Fig.  146 


X-ray  January  29,  1907. 

On  January  29,  1907,  the  accompanying  .r-ray  was 
taken  of  a  patient  suffering  from  every  symptom  of  pyor- 
rhoea including  constitutional  disorders.     This  radiograph 

Fig.  147 


X-ray  May  30,  1912. 


was  sent  to  Mr.  C.  Clark,  of  London,  with  the  patient  on 
May  30,  1912,  with  a  request  to  produce  a  picture  of 
the  same  parts.  The  result  will  be  seen  in  the  .r-ray,  Fig. 
147.    It  will  be  seen  that  the  alveolus  has  changed  in  five 


294 


ELECTRO-THERAPEUTICS 


and  one-half  years  considerably,  between  the  second  premolar 
and  the  cuspid  carrying  a  bridge,  it  is  quite  a  different  con- 
tour, it  is  a  higher  level,  there  is  more  alveolar  process  about 
the  molar  roots,  and  the  posterior  boundary  of  the  last  molar 
has  a  growth  of  alveolus  resembling  a  molar,  which  is  new 
bone.  Allowing  for  a  slight  difference  of  angles  at  which 
the  radiographs  were  taken,  there  is  still  a  marked  differ- 
ence in  the  appearance  of  the  bone,  the  first  shows  marked 
decalcification  and  morbid  changes,  the  second  shows  a 
reformation  of  bone  about  the  roots  of  the  teeth.  The 
clinical  changes  are  no  less  marked,  the  pyorrhea  has 
entirely  disappeared,  the  gums  are  healthy  and  the  teeth 
firm.     The  pyorrhea  was  treated  with  zinc  ions. 

Fig.  148 


X-ray,  December  7,  1906. 

Another  example  is  shown  in  Fig.  148;  .T-ray  taken  on 
December  7,  1906,  which  shows  pyorrhoea  started  about 
the  superior  incisors;  this  case  was  treated  with  zinc  ions. 
The  a>ray  taken  on  June  6,  1912,  shows  that  no  change 
has  taken  place  in  the  bone  surrounding  the  roots  of  the 
teeth,  except  possibly  a  denser  calcification.  This  appear- 
ance, however,  may  be  due  to  the  difference  in  length  of 
time  in  exposure  when  taking  the  .T-ray,  but  the  loss  of 


TREATMENT  OF  PYORRHCEA  ALVEOLARIS       295 

bone  was  no  more  than  it  was  six  years  previously.  The 
progress  of  the  pyorrhoea  has  been  checked  by  a  few  treat- 
ments of  zinc  ionization  and  subsequent  half-yearly  treat- 
ments which  consisted  chiefly  in  thoroughly  cleaning  the 
teeth. 

Fig.  149 


X-ray,  June  6,  1912. 
Fig.  150 


X-ray,  January  29,  1907. 


The  next  .r-ray  taken  January  29,  1907,  shows  a  bad  case 
which'  has  been  cured,  and  the  discharge  has  not  returned 
since  treatment  five  and  one-half  years  ago,  although  it  has 
required  constant  attention  to  keep  it  from  relapse,  owing 


296 


ELECTRO-THERAPEUTICS 


to  the  faulty  articulation  and  constant  irritation  thereby. 
It  will  be  seen  that  the  teeth  in  the  second  #-ray  (taken 
May  30,  1912)  have  been  ground  on  the  occluding  sur- 
faces to  correct  this.  The  teeth  are  functional  and  not 
loose,  as  would  be  expected  by  the  appearance  of  these 
radiographs. 

Fig.  151 


X-ray,  May  30,  1912. 


It  makes  the  greatest  difference  to  people  affected  with 
pyorrhoea  to  this  extent  if  by  treatment  they  are  able  to 
retain  their  teeth  for  years,  and  are  saved  the  wearing  of 
plates,  which  usually  act  as  irritants  and  lead  to  the  loss  of 
the  entire  denture  from  progressive  periodontal  disease. 

A  healthy  fibrous  tissue  forms  about  the  teeth  in  these 
cases  which  holds  them  firmly  in  position,  and  if  kept  from 
bacterial  infection  (as  they  can  be  by  ionic  medication) 
they  are  retained  and  are  functional. 

It  must  not  be  thought  that  the  disease  is  curable  at 
any  stage  by  simply  ionizing  the  periodontal  tissue  and 
alveolus.  There  are  many  conditions  which  arise  that 
defy  all  treatment.  It  is  difficult  to  formulate  any  rule 
to  classify  the  teeth  which  should  not  be  treated  by  any 
other  means  than  by  extraction.  As  a  general  rule  it  is 
never  necessary  or  advisable  to  extract  a  whole  set  of  teeth 
because  a  few  are  hopelessly  involved  and  the  rest  only 
slightly  affected.     Teeth  in  which  septic  infection  has  ex- 


TREATMENT  OF  PYORRHEA  ALVEOLARIS        297 

tended  to  the  apices  destroying  the  pulp  and  causing  ab- 
sorption of  the  end  of  the  roots  should  be  extracted.  When 
pockets  extend  to  the  bifurcation  of  multiple  rooted  teeth, 
the  sterilization  of  these  surfaces  is  usually  very  transitory 
and  reinfection  occurs  principally  from  stagnation  of  food. 
Many  mechanical  appliances,  such  as  splints,  are  useful 
auxiliaries  to  ionic  treatment  and  precautions  in  correct- 
ing faulty  articulation,  replacing  teeth  which  have  been 
displaced,  supplying  missing  teeth,  and  many  other  such 
methods  which  contribute  greatly  to  successful  treatment 
of  pyorrhoea  alveolaris,  should  accompany  this  treatment, 
which  deals  principally  with  the  bacteria  phase  of  the 
disease. 


CHAPTER  XV. 

ELECTRICITY  FOR  ANESTHESIA,  FOR  BLEACH- 
ING, AND  FOR  NEURALGIA. 

Anaesthesia  of  Sensitive  Dentine — For  Immediate  Extirpation — Anaes- 
thesia of  Gums  and  Alveolus — Electric  Tooth  Bleaching — Bleaching  with 
Chlorinated  Lime — Bleaching  with  Hydrogen  Dioxide — Neuralgia. 

ANESTHETIC  APPLIED  BY  ELECTRIC  CURRENT. 

Anaesthesia  of  Sensitive  Dentine. — The  anaesthetic  effect  of 
cocaine  on  sensitive  dentine  when  applied  by  the  electric 
current  is  well  known.  In  America  the  interest  of  the 
dental  profession  was  attracted  to  this  subject  by  W.  J. 
Morton  in  1896,  who  attributed  the  effects  to  cataphoresis. 
A  mass  of  literature  has  since  appeared  from  time  to  time 
setting  forth  the  advantages  and  disadvantages  of  anaes- 
thesia of  dentine  by  electrical  application  of  cocaine. 

The  use  of  the  current  for  this  purpose  has  often  been 
brought  into  disrepute  by  the  lack  of  knowledge  of  general 
electro-therapeutics.  Cataphoresis  (see  Part  II,  Cata- 
phoresis) has  been  the  only  effect  thought  of,  and  it  has 
not  been  realized  that  cocaine  ions  penetrate  dentine  with 
a  very  low  current  strength,  and  that  if  the  electrical  ap- 
plication of  the  drug  is  pressed  too  far  complete  anaesthesia 
of  the  pulp  takes  place,  when  it  may  be  only  desired  to 
benumb   the   sensitive   surface   of  the   dentine. 

As  has  been  pointed  out  already  in  this  work  the  effect 
of  the  electric  current  on  cocaine  is  not  an  electro-osmotic 
effect  in  the  sense  of  propelling  the  solution  of  cocaine 
en  masse  into  the  dentinal  tubuli  by  cataphoresis,  but  it 
is  ionic  in  the  sense  that  the  particles  of  cocaine  are  dis- 


ANESTHESIA   OF  DENTINE  299 

sociated  in  the  solution  containing  them,  and  being  elec- 
trically charged  are  conveyed  by  conduction  into  the 
organic  structure  of  the  dentine  on  which  it  has  an  anaes- 
thetic effect.  The  depth  of  penetration  of  cocaine  ions 
will  depend  on  the  organic  structure  of  the  tooth  and  the 
current  strength  which  is  used. 

Fig.  152 


Imperfect  technique. 

Cocaine  ions  penetrate  the  superficial  layer  of  sensitive 
dentine  with  a  current  strength  of  only  0.5  ma.  and  produce 
anaesthesia.  With  a  stronger  current  the  effect  is  more 
rapid  and  the  penetration  is  deeper.  Failure  to  produce 
the  anaesthetic  effect  in  a  few  minutes  is  usually  due  to 
faulty  technique.  If  the  electrode  is  placed  on  a  surface 
of  dentine  so  that  the  current  is  only  passed  from  a  small 
area  (see  Fig  152),  the  area  in  contact  with  the  metallic 
conductor  only  will  be  affected  by  the  passing  of  cocaine 
ions,  and  penetration  will  be  greatest  at  the  point  of  con- 
tact. In  order  to  obtain  perfect  anaesthesia  of  the  whole 
surface  which  it  is  desired  to  affect,  the  electrode  should 
cover  the  whole  area.  This  insures  the  passing  of  ions  into 
all  the  organic  matter  exposed  to  conduction  of  current, 
and  the  larger  the  area  the  less  painful  will  the  process 
be,  as  the  density  will  be  lessened  by  the  increase  of  area 
of  the  electrode. 


300  ELECTRO-THERAPEUTICS 

To  anaesthetize  dentine  in  the  cavity  of  a  tooth,  a  10 
to  20  per  cent,  aqueous  solution  of  codraline,  novacocaine, 
cocaine,  or  any  of  the  cocaine  preparations  now  in  use, 
should  be  placed  into  the  cavity  on  a  pellet  of  cotton 
wool  and  should  be  warmed  to  99°  F.  On  this  should 
be  fitted  a  piece  of  platinum  foil  sufficiently  large  to  cover 
the  whole  area  of  the  cavity,  and  to  this  applied  a  platinum 
anode.  The  current  should  be  turned  on  gradually  until 
it  is  felt  by  the  patient,  when  it  should  be  allowed  to  pass 
for  a  minute,  and  increased  until  again  felt.  Except  it  is 
desired  to  anaesthetize  the  pulp,  current  should  never  be 
raised  to  the  strength  of  4  ma.,  for  should  it  be  possible  to 
pass  this  amount  of  current  without  pain  the  pulp  will 
then  be  found  to  be  anaesthetized  and  can  be  drilled  without 
pain. 

A  point  in  technique  which  has  already  been  insisted 
upon,  but  which  may  not  have  been  especially  noticed,  is 
here  again  referred  to,  i.  e.,  when  a  voltic  cell  battery  is 
used  it  should  never  be  of  that  kind  which  is  provided 
with  a  "current  collector"  alone,  if  it  has  a  current  col- 
lector (that  is,  a  switch  with  studs  representing  each  cell 
of  the  battery)  it  should  also  have  a  finely  graded  rheostat 
of  graphite  or  German  silver  wire  with  sliding  contact, 
which  permits  of  only  a  fraction  of  a  volt  increase  of  E.  M. 
F.  when  the  resistance  is  decreased  by  moving  the  shunt 
of  the  rheostat,  the  current  strength  will  then  be  increased 
by  a  fraction  of  a  milliampere,  and  no  shock  is  possible 
with  this  gradual  increase  of  current.  If  stud  contact 
points  are  used  alone,  at  contact  with  each  stud  the  E.  M. 
F.  is  increased  by  1  volt  in  some  batteries  and  by  1.5  volts 
in  others,  according  to  the  voltage  of  the  cells  composing 
them.  This  means  that  the  current  strength  is  also  abruptly 
increased  as  will  be  indicated  by  the  milliampere  meter, 
according  to  the  resistance  in  circuit.  In  soft  tissues  like 
periodontal  tissue  increase  of  1  volt  will  sometimes  in- 
crease the  current  strength  considerably.  In  dentine, 
owing  to  the  great  resistance  of  that  tissue,  the  increase 
might  be  only  0.1  ma.,  but  the  shock  of  sudden  increase  of 
E.  M.  F.  is  even  more  severe  than  in  soft  tissues. 


ANJESTHESIA   OF   THE   PULP  301 

It  is  undesirable  to  anaesthetize  a  pulp  except  it  is  to  be 
extirpated,  for  in  some  cases  it  dies  subsequently,  apparently 
from  the  effects. 

The  influence  of  the  current  upon  pulps  which  have 
been  anaesthetized  is  a  debatable  point.  It  has  been 
pointed  out  by  some  authorities  that  the  death  of  the  pulp 
may  ensue,  by  others  that  no  ill  effects  take  place.  Dr. 
Louis  Jack1  states  "in  deep  cavities  nearing  the  pulp,  the 
effect  extends  to  that  organ.  The  recurrence  of  sensitivity 
takes  place  within  a  few  hours.  No  injury  appears  to 
follow."  This  may  not  always  be  the  case.  In  some  cases 
if  anaesthesia  is  pressed  to  the  point  that  the  pulp  is 
anaesthetized  the  subsequent  death  of  the  pulp  takes  place. 
There  is  a  scientific  electrical  reason  for  expecting  this 
result,  which  has  been  demonstrated  by  experiment  and 
in  practice.  If  a  platinum  electrode  is  placed  in  albumin 
and  a  current  of  2  to  3  ma.  passed,  coagulation  takes  place 
about  the  electrode.  The  electro-positive  effect  on  blood 
is  also  to  coagulate  it;  this  effect  is  obtained  in  the  treat- 
ment of  aneurysm  by  electrolysis.  If  the  albuminous 
ingredient  of  the  pulp  be  coagulated  by  the  passing  of  the 
current,  which  would  undoubtedly  be  the  case  if  4  or  5  ma. 
of  current  is  passed,  the  effect  would  be  stasis  and  death 
of  the  pulp  in  the  majority  of  cases.  The  cocaine  would 
be  absorbed  and  taken  into  the  general  circulation,  and  is 
not  an  element  of  danger  in  this  respect. 

The  opinion  that  coagulation  of  albumin  is  the  effect 
accountable  for  the  death  of  the  pulp,  when  it  occurs  after 
cocaine  anaesthesia  is  simply  one  of  conjecture  yet  to  be 
proved. 

Dr.  Finzi2  points  out  that  when  cocaine  is  driven  into 
the  skin  with  an  electrode  3x3  cm.  with  a  current  strength 
of  10  to  15  ma.  for  ten  minutes,  anaesthesia  of  the  area 
treated  of  a  very  transitory  nature  is  produced,  but  is  fol- 
lowed  by    hyperesthesia   and   hyperemia,  which  persists  for 


1  Text-book  on  Operative  Dentistry  (Kirk),  p.  167. 

2  British  Medical  Journal,  November  2,  1912. 


302  ELECTRO-THERAPEUTICS 

days.  If  this  effect  is  also  produced  on  the  pulp  tissue 
it  would  be  sufficient  to  cause  death  of  the  pulp.  The 
epidermis  being  of  very  different  vascular  construction  from 
pulp  tissue,  hyperesthesia  and  hyperemia  may  possibly  be 
averted  by  vascular  absorption,  and  death  of  the  pulp 
avoided  in  many  cases;  still  there  is  the  liability,  from  one 
cause  or  another,  of  death  of  the  pulp  to  follow  cocaine 
anaesthesia  by  electrotherapy. 

For  Immediate  Extirpation. — For  immediate  extirpation 
of  the  pulp  of  a  sound  tooth  a  small  opening  should  be 
made  through  the  enamel  opposite  the  nearest  point  to 
the  pulp.  When  sensitive  dentine  is  reached  the  drill 
hole  should  be  lined  with  a  pellet  of  cotton  wool  saturated 
with  the  anaesthetic  and  to  this  applied  a  platinum  electrode 
of  about  the  diameter  of  the  hole;  0.5  to  1  ma.  current  should 
then  be  passed  from  the  positive  pole  for  a  few  minutes, 
at  the  termination  of  that  time  it  will  be  possible  to  drill 
deeper  toward  the  pulp,  and  if  still  sensitive  a  similar 
application  should  be  made,  slowly  increasing  the  current 
strength  to  3  or  4  ma.  This  will  ensure  the  possibility  of 
opening  the  pulp  chamber;  then  a  further  application  for 
a  minute  will  produce  complete  anaesthesia  of  the  pulp. 
The  electrode  in  this  operation  should  be  pressed  firmly 
into  position  and  kept  steadily  there,  so  as  not  to  vary  the 
resistance  which  in  dentine  is  considerable  owing  to  the 
small  amount  of  organic  matter.  The  current  should  be 
turned  off  before  removing  the  electrode. 

The  ordinary  precaution  of  isolating  the  tooth  and 
keeping  away  saliva  by  application  of  rubber  dam  is 
advisable,  although  it  is  not  always  necessary  to  apply 
the  rubber  dam.  Excess  of  cocaine  may  produce  toxic 
effects  by  leaking  into  the  soft  tissue  about  the  necks  of 
the  teeth,  or  by  the  passing  of  ions  into  the  circulation 
through  the  pulp  itself.  It  is  therefore  advisable  to  use 
some  cocaine  extract  which  contains  adrenalin  chloride, 
or  the  least  toxic  of  cocaine  compounds,  and  see  that  no 
leaking  occurs. 

The  operation  of  stapling  or  splinting  incisors  in  pyor- 


BLEACHING  OF   THE   TEETH  303 

rhoea  cases  is  greatly  facilitated  by  this  method  of  anaesthet- 
izing the  dentine  and  pulp.  It  is  often  advisable  to  remove 
the  pulp  from  pyorrhoea  teeth  which  are  to  be  stapled. 
This  can  be  readily  done  by  exposing  the  dentine  in  prox- 
imity of  the  pulp  in  the  position  of  the  receptacle  for  the 
pins  necessary  to  form  the  staple.  Then  the  teeth  can  be 
anaesthetized  with  codreline,  using  a  current  of  3  to  4  ma. 

In  cases  of  inflammation  of  an  exposed  pulp  when  pres- 
sure anaesthesia  is  often  impossible,  cocaine  ions  can  be 
used  to  produce  complete  anaesthesia.  The  conduction 
of  current  is  the  same  in  inflamed  tissue  as  in  healthy 
tissue,  and  ions  migrate  just  as  effectively  in  one  as  the 
other.  When  the  pulp  is  exposed,  a  minimum  of  0.2  ma. 
current  may  be  all  that  can  be  tolerated,  but  ions  are 
formed  even  at  this  low  current  strength,  and  it  will  be 
found  that  after  a  minute  or  two  of  passing  this  current 
it  is  possible  to  increase  the  strength  gradually  until  anes- 
thesia ensues,  when  3  or  4  ma.  can  be  passed  without  dis- 
comfort. 

Anaesthesia  of  the  Gums  and  Alveolus. — Anaesthesia  of 
the  gums  and  alveolus  for  extraction  can  be  successfully 
carried  out  by  Dr.  W.  J.  Morton's1  method  of  applying 
a  metallic  lined  rubber  cup  electrode  to  both  sides  of  the 
gums  about  the  teeth,  but  this  method  is  more  difficult  and 
less  sure  for  this  purpose  than  hypodermic  injections  as  now 
generally  practised. 


ELECTROLYTIC  TOOTH  BLEACHING. 

Discoloration  of  teeth  due  to  chemical  changes  of  the 
organic  contents  of  the  dentinal  tubuli  and  also  absorption 
by  the  tubuli  of  putrefactive  products  of  the  dead  pulp 
tissue  provides  one  of  the  knotty  problems  which  often 
taxes  the  skill  of  the  careful  and  ingenious  operator  to  the 
utmost.     The  subject  of  the  chemistry  of  tooth  discolora- 

1  Cataphoresis,  p.  222. 


304  ELECTRO-THERAPEUTICS 

tion  has  been  ably  expounded  by  Dr.  E.  C.  Kirk,1  who  states 
that  "the  proteid  elements  of  the  pulp  tissue  are  complex 
combinations  of  carbon,  oxygen,  hydrogen,  nitrogen, 
sulphur,  and  phosphorus,  which  in  the  gradually  breaking 
down  of  the  process  of  putrefactive  decomposition  are 
split  up  finally  into  dioxide,  water,  ammonia,  and  hydrogen 
sulphide,  with  possibly  the  formation  of  traces  of  phosphatic 
salts."  The  principle  of  bleaching  teeth  should  aim  at 
the  transfer  of  this  chemical  combination  which  causes  the 
discoloration,  into  a  new  combination  by  the  addition  of  a 
fresh  molecule,  which  has  the  property  of  combining  to 
form  a  compound  of  transparent  or  translucent  appear- 
ance. This  fresh  molecule  has  long  been  known  to  be 
oxygen  in  its  nascent  state,  the  difficulty  has  been  to  pro- 
cure it  and  to  transmit  it  to  the  dentine  tubuli  containing 
discolored  organic  matter. 

The  most  effective  bleaching  agents  are  calcium  hypo- 
chloride  or  chlorinated  lime,  chlorinated  soda,  hydrogen 
dioxide,  sodium  dioxide,  and  pyrozone  (an  ethereal  solution 
of  H2O2).  All  these  can  be  applied  to  the  dentine  of  dis- 
colored teeth  for  their  bleaching  qualities  more  effectively 
with  an  electric  current  than  without. 

Bleaching  with  Chlorinated  Lime. — The  general  principles 
of  technique  in  bleaching  have  been  referred  to  under 
that  heading  in  another  part  of  this  work  and  must  be 
observed  in  the  bleaching  operation.  The  tooth  must 
be  prepared  so  that  the  two  electrodes  can  be  placed  in  it 
a  little  distance  apart,  but  not  separated  by  a  portion  of 
tooth  structure;  there  should  be  liquid  contact  completing 
the  circuit  between  the  two  poles.  Fig.  153  is  a  diagram 
illustrating  the  electrical  contact  in  a  central  incisor.  A 
is  the  orifice  of  the  opening  into  the  pulp  chamber  which 
has  been  enlarged  internally  as  indicated  by  the  dotted 
line  C,  into  which  is  placed  the  -f-  platinum  electrode.  B 
is  a  small  drill  hole  in  which  is  placed  the  —  platinum 
electrode.      D  is  a  small  opening  made  between  A  and  B 

1  Text-book  of  Operative  Dentistry,  p.  524. 


BLEACHING  OF   THE   TEETH 


305 


to  complete  liquid  contact  and  thereby  reduce  resistance 
effects.  If  the  tooth  is  filled  or  decayed  at  an  approximal 
surface  this  position  should  be  utilized  for  introducing  the 
second  electrode  (as  shown  in  Fig.  154).  Into  the  cavity, 
between  the  metallic  conductors,  should  be  placed  a  pellet 
of  cotton  wool  in  the  meshes  of  which  has  been  incorpor- 
ated a  pasty  mixture  of  chlorinated  lime  and  2  per  cent, 
sodium  sulphate.  The  circuit  should  be  established  by 
gradually  turning  on  the  current  until  5  ma.  are  measured 
on  the  milliampere  meter.  By  the  electrolytic  action  nas- 
cent oxygen  is  eliminated  at  the  positive  pole  and  hydrogen 
and  chlorine  at  the  negative,   at  the  same  time  electro- 


Fig.   153 


Fig.    154 


lysis  of  water  takes  place,  H2  molecules  accumulate  at  the 
negative  and  O  at  the  positive  electrode.  The  chemical 
action  which  takes  place  by  the  passing  of  the  current 
furnishes  a  large  supply  of  nascent  oxygen,  chlorine,  and 
hydrogen.  The  chlorine  has  a  great  affinity  for  hydrogen, 
with  which  it  combines  freely.  The  positively  charged 
atoms  H-2  +  Cl2  migrate  to  the  negative  pole,  where  they 
give  up  their  charge  of  electricity  to  the  electrode  and  unite 
to  form  2HC1  (hydrochloric  acid),  the  negatively  charged 
atom  O  migrates  to  the  positive  electrode,  where  it  unloads 
its  charge  of  electricity  and  O  is  eliminated.  By  this  means 
a  large  quantity  of  oxygen  is  liberated  in  contact  with 
20 


306  ELECTRO-THERAPEUTICS 

the  dentinal  tubuli,  the  hydrogen  which  would  unite  with 
it  to  form  water  is  utilized  by  the  chlorine  atom  which 
leaves  the  nascent  oxygen  free  to  combine  with  organic 
matter  in  the  tubuli  of  the  dentine. 

The  action  of  these  gases  is  hastened  and  increased  by 
the  evolution  of  heat  which  takes  place  during  the  pass- 
ing of  the  current,  the  electrodes  which  should  be  thin 
platinum  wire  (0.5  mm.  diameter  respectively),  become 
heated  when  the  electro-motive  force  is  about  20  volts 
passing  a  current  of  about  5  ma.  This  heating  effect  can 
be  increased  by  either  diminishing  the  size  of  one  electrode 
or  by  increasing  the  E.  M.  F.  to  30  volts  passing  10  ma. 
By  this  means  the  tooth  structure  can  be  heated  con- 
siderably, which  assists  the  bleaching  effect  by  increasing 
oxidation. 

When  bleaching  is  almost  completed  in  the  body  of  the 
tooth  a  fresh  supply  of  bleaching  mixture  should  be  placed 
in  the  tooth  and  the  poles  of  the  battery  or  switchboard 
reversed,  to  complete  the  process  about  that  part  which 
formerly  contained  the  negative  electrode. 

It  will  be  noticed  that  during  the  bleaching  operation 
by  this  method  very  little  chlorine  gas  escapes,  and  the 
odor  of  chlorine  is  very  faint.  This  is  most  likely  due  to 
the  perfect  union  of  Cl2  +  H2  in  the  formation  of  2HC1 ; 
on  the  other  hand,  if  a  weak  solution  of  sulphuric  acid  be 
used  as  the  solution  electrode  with  chlorinated  lime,  the 
pungent  odor  of  chlorine  gas  is  distinctly  observed. 

The  canals  of  all  teeth  which  are  bleached  with  chlorin- 
ated lime  should  be  previously  sealed  at  their  apices  with 
gutta-percha.  There  are  some  precautions  which  should 
be  observed  when  electrodes  approximate  each  other  so 
closely  as  here  described.  The  wires  should  be  properly 
insulated  to  prevent  short  circuiting;  the  solution  elec- 
trode in  the  tooth  should  be  replenished  when  necessary, 
if  it  becomes  dry  the  resistance  to  current  is  much  in- 
creased and  heat  is  increased;  one  electrode  should  be 
made  fast  in  the  tooth  by  some  mechanical  contrivance, 
and  should  be  made  secure  in  position    before  attaching 


BLEACHING  OF   THE   TEETH  307 

the  conducting  wire  to  it,  if  it  is  bent  into  a  hook  at  the 
end  as  shown  in  the  diagram  (Fig.  154)  the  conducting  wire 
can  be  readily  attached;  the  operator  should  control  the 
other  electrode.  After  bleaching,  all  traces  of  the  products 
of  electrolysis  and  the  bleaching  agent  should  be  removed, 
and  the  cavity  wiped  out  with  a  solution  of  bicarbonate 
of  soda  or  ammonia  water. 

Bleaching  with  Hydrogen  Dioxide. — The  bleaching  with 
hydrogen  dioxide,  sodium  dioxide,  and  pyrozone  with  the 
electric  current  are  so  similar  in  chemical  action  and  effect 
that  all  can  be  described  under  the  same  heading. 

In  the  case  of  sodium  dioxide  the  migration  of  sodium 
ions  (which  are  colorless)  takes  place  to  the  +  pole. 

The  method  of  applying  both  electrodes  to  the  tooth 
already  described  is  very  effective  in  the  use  of  H202  prepara- 
tions. The  current  strength  necessary  to  eliminate  oxygen 
gas  by  this  technique  is  reduced  to  a  minimum  and  the 
resistance  of  the  body  in  circuit  is  eliminated;  moreover, 
heat  can  be  produced  in  the  tooth  without  discomfort, 
which  is  a  valuable  auxiliary. 

The  H202  solution  should  be  placed  in  the  cavity  on 
cotton  wool  between  the  electrodes;  on  passing  the  current 
large  quantities  of  gas  is  evolved  at  both  electrodes;  the 
H  atoms  migrate  to  the  negative  electrode  and  0  to  the 
positive.  After  operating  with  the  current  passing  in 
one  direction  for  five  to  eight  minutes  the  poles  should  be 
reversed  and  current  passed  in  the  opposite  direction. 
In  addition  to  liberating  the  very  loosely  combined  oxygen 
atom  in  H2O2  solution,  electrolysis  of  H20  takes  place, 
which  supplies  a  further  atom  of  nascent  oxygen  for  action 
on  organic  matter  in  the  dentine.  In  teeth  of  young  sub- 
jects and  recently  discolored  teeth  the  electrolytic  bleaching 
action  of  the  H2O2  is  very  rapid. 

To  facilitate  electrical  conduction  in  H202  preparations, 
the  addition  of  10  parts  in  100  of  2  per  cent,  solution  of 
sodium  chloride  or  sulphate  should  be  made;  and  in  the 
case  of  ethereal  solution  of  pyrozone  the  ether  should  be 
evaporated  over  a  hot-water  bath  after  adding  a  similar 
volume  of  2  per  cent,  sodium  sulphate. 


308  ELECTRO-THERAPEUTICS 


NEURALGIA. 


The  term  neuralgia  is  applied  to  a  painful  affection  of 
either  the  course  of  a  nerve  or  the  area  of  its  distribu- 
tions. It  is  a  condition  of  pain,  which  in  the  early  stages 
may  amount  to  mere  flashes  of  pain  responding  to  some 
afferent  impulse  set  up  by  an  irritant  in  a  remote  part,  but 
later  a  more  lasting  and  severe  pain  results  in  consequence 
of  continual  irritation  of  the  nerves  responsible  for  the 
reflex  action.  Trifacial  or  trigeminal  neuralgia  which 
occurs  in  connection  with  the  fifth  nerve  is  constantly 
brought  to  our  notice  in  its  many  phases.  Diagnosis  of 
the  cause  of  facial  neuralgia  when  the  teeth  are  responsible 
for  the  irritation  setting  up  this  reflected  pain  in  one  of  the 
facial  segmented  areas  is  often  difficult,  but  much  is  done 
by  the  dentist  in  his  daily  practice  to  arrest  and  relieve 
this  form  of  pain.  Nevertheless,  obscure  cases  arise  which 
defy  the  skill  of  the  medical  and  dental  professions,  es- 
pecially that  form  of  neuralgia  known  as  tic  douloureux, 
which  is  not  ordinary  "referred  neuralgia"  but  is  often 
regarded  as  a  diseased  state  of  the  Gasserian  ganglion  or  a 
large  branch  of  the  fifth  nerve. 

Facial  neuralgia  is  often  caused  from  septic  periodon- 
titis and  indirectly  from  the  effects  of  this  disease;  the 
sensitive  necks  of  teeth  are  exposed  to  the  irritating  influ- 
ences of  external  agents  which  provide  constant  and  more 
or  less  severe  afferent  stimuli  to  be  sent  out  from  the 
surfaces  of  the  teeth,  these  sensitive  surfaces  are  peripheral 
endings  of  the  fifth  nerve,  which  are  exposed  and  convey 
painful  impulses  to  the  nerve  trunk  or  Gasserian  ganglion, 
resulting  in  reflex  neuralgia.  This  form  of  reflected  pain  is 
exceedingly  common  among  patients  suffering  from  pyor- 
rhoea alveolaris,  and  the  question  of  treating  the  disease 
should  include  the  possibility  of  relieving  this  phase.  It  is 
often  the  case  that  acute  neuralgia  follows  the  operation 
of  scaling  the  teeth  and  many  patients  suffer  from  constant 
facial  neuralgia  who  have  so-called  "dry  pyorrhoea." 


NEURALGIA  309 

The  author  has  noticed  with  considerable  satisfaction 
the  remarkable  effect  on  neuralgia  which  is  caused  by  sen- 
sitive surfaces  of  teeth,  by  their  treatment  with  zinc  ions. 
Many  cases  of  persistent  and  long-standing  neuralgia  in 
the  maxillary,  temporal,  fronto-temporal,  and  mandibular 
areas  have  completely  disappeared  after  treatment  of 
pyorrhoea  with  zinc  ions  and  silver  ions.  In  the  treat- 
ment of  these  cases  the  application  of  the  current  at  first 
causes  neuralgic  pains  in  the  reflected  area  from  which 
the  patient  generally  suffers  or  corresponding  to  the  area 
influenced  by  the  particular  teeth  to  which  the  current  is 
applied,  and  it  is  often  impossible  to  apply  more  than  a 
very  weak  current,  0.5  or  1  ma.,  but  when  the  pyorrhoea 
is  cured  at  subsequent  treatments  it  is  the  experience  of 
the  writer  that  the  sensitiveness  of  the  exposed  necks  of 
teeth  becomes  less,  the  neuralgia  is  relieved,  and  teeth 
which  were  formerly  painful  when  1  ma.  current  was  ap- 
plied are  painless  with  3  to  4  ma.  The  relief  to  neuralgia 
is  usually  very  prompt,  although  the  relief  to  the  sensitive 
surface  of  the  teeth  is  slow  and  may  not  be  complete,  as 
far  as  passing  current  is  concerned,  for  several  years,  but 
the  ultimate  effect  in  this  respect  is  sure  and  most  notice- 
able from  a  clinical  standpoint. 

In  the  treatment  of  exposed  roots  of  molars,  especially 
in  the  palatal  aspect  of  maxillary  and  approximal  surfaces 
of  mandibular  molars,  the  application  of  silver  ions  from  a 
weak  aqueous  solution  of  silver  nitrate  is  very  rapid  in 
removing  sensation  from  these  surfaces  and  the  effect  is 
permanent. 

The  only  construction  that  can  be  placed  on  the  action 
of  the  ion  in  this  respect  is  that  it  passes  into  the  organic 
structure  of  the  dentine  and  cementum  by  conduction, 
the  penetration  is  into  the  protoplasm  of  the  cell,  where 
the  effect  of  the  ion  is  far  more  complete  than  if  the  drug 
were  applied  as  tincture  or  liniment  painted  on  the  surface; 
the  action  in  the  latter  case  is  only  superficial  and  pene- 
tration at  the  best  very  imperfect.  When  we  consider 
that   by   the    electrolytic    effect    the    molecules    are    split 


310  ELECTRO-THERAPEUTICS 

and  the  ions  are  conveyed  by  its  electrical  charge  along  a 
definite  path  of  conduction,  which,  in  so  dense  a  structure 
as  dentine,  provides  no  means  of  circulatory  absorption 
of  the  dissociated  salt,  the  medicamental  effect,  if  pro- 
duced at  all,  must  be  of  a  lasting  nature.  Chloride  of 
zinc  and  silver  nitrate  as  metallic  salts  in  solution  have 
long  been  known  to  have  obtunding  effects  on  sensitive 
dentine,  but  much  of  the  good  effects  are  lost  in  ordinary 
applications  for  the  lack  of  penetration.  With  electrical 
application  we  are  provided  with  just  that  which  is  lacking 
to  obtain  the  desired  effect. 

Septic  infection  of  the  oral  cavity  is  accounted  by  some 
authors  to  be  the  principal  cause  of  facial  neuralgia  arising 
from  fifth  nerve  reflexes,  and  it  can  be  readily  conceived 
that  constant  afferent  impulses  directed  to  the  nerve 
centres  from  the  seat  of  such  general  irritation,  accompanied 
by  the  general  constitutional  depression  and  lowering  of 
the  tone  of  the  system  by  absorption  of  septic  matter, 
would  be  the  cause  of  nerve  excitability  and  even  disease 
of  nerve  centres  directly  connected. 

But  the  sensitive  condition  of  soft  tissue  in  periodontal 
disease  is  not  as  frequently  the  irritant  responsible  for 
reflected  pain  as  is  the  sensitive  surface  of  the  teeth  them- 
selves, which  are  liable  to  cause  reflex  pain  from  influences 
that  do  not  affect  the  soft  tissues,  such  as  thermal  changes, 
sweets,  or  sours. 

In  treating  sensitive  pyorrhoea  teeth  a  flat  zinc  electrode 
of  large  enough  area  to  cover  the  whole  surface  of  a  mandi- 
bular incisor  should  be  wrapped  with  cotton  wool  which 
is  saturated  with  5  per  cent,  zinc  chloride  warmed  to  90° 
Fahrenheit,  the  electrode  should  be  firmly  pressed  to  the 
surface  of  the  tooth  and  the  current  turned  on  very  grad- 
ually until  felt  by  the  patient;  by  keeping  it  steady  it  is 
often  possible  to  use  more  current,  the  current  should  be 
turned  off  slowly  after  a  few  minutes  and  the  operation 
repeated  on  another  tooth.  These  teeth  are  very  sus- 
ceptible to  shock  from  sudden  alteration  of  the  E.  M.  F. 
and  great  care  is  necessary  in  using  the  current.     Perio- 


NEURALGIA  311 

dontal  and  gum  tissue  can  be  treated  at  the  same  time  by 
passing  the  point  of  the  electrode  under  the  gum;  the 
number  of  treatments  and  the  time  occupied  correspond 
with  the  method  of  treating  septic  periodontitis  already 
described. 

Neuralgic  pain  referred  to  in  connection  with  perio- 
dontal disease  is  usually  slight  and  transient,  but  occurs 
frequently  and  is  the  cause  of  much  discomfort  to  the 
patient,  who  will  complain  of  it.  A  more  severe  form  of 
facial  neuralgia  which  is  probably  developed  from  long 
standing  and  everlasting  repetition  of  the  slighter  form, 
is  well  known  to  the  medical  world.  The  sufferings  of  the 
patients  in  these  cases  are  intense  and  the  medical  man 
is  usually  consulted.  The  electrical  treatment  of  these 
cases  has  met  with  considerable  success.  The  principle 
of  counter-irritation  is  carried  out  with  a  continuous  cur- 
rent applied  with  electrodes  of  large  area  and  a  current  of 
considerable  intensity.  The  active  electrode  is  applied  to 
the  whole  surface  of  one  side  of  the  face  in  close  contact 
with  the  skin,  it  is  E-shaped,  which  leaves  apertures  for 
eye  and  mouth.  The  indifferent  electrode  also  of  large 
area  is  placed  at  the  back  of  the  neck.  A  current  of  30  to 
80  ma.  is  passed  for  half  an  hour  at  a  time  every  day  or 
every  other  day,  diminishing  the  current  as  the  neuralgic 
symptoms  become  less.  Good  results  are  claimed  for  this 
method  of  treatment  when  the  neuralgia  is  of  local  origin. 
Leduc1  has  reported  the  successful  use  of  salicylic  and 
quinine  ions  introduced  electrically  by  much  the  same 
technique  as  just  described.  The  method  is  quite  new  but 
the  results  already  obtained  in  severe  trigeminal  neuralgia 
should  lead  to  its  general  use  in  these  cases,  especially 
when  other  forms  of  treatment  have  failed.  Dr.  R.  W. 
Mackenna  reported  a  case  of  immediate  relief  of  neuralgia 
by  the  use  of  salicylic  ions  with  a  comparatively  low  cur- 
rent. He  says:  "I  have  had  remarkable  proof  of  the  effi- 
cacy of  the  saliclyic  ion  in  the  treatment  of  neuralgia  fol- 

1  Archives  d'Electricite  Med.,  July  25,  1904. 


312  ELECTRO-THERAPEUTICS 

lowing  herpes.  The  patient  had  not  slept  for  four  nights 
because  of  the  intense  pain,  but  found  relief  after  the  ions 
from  a  2  per  cent,  solution  of  salicylate  of  soda  had  been 
carried  into  the  affected  zone  by  a  current  of  7  to  11  ma. 
for  thirty  minutes.  She  was  able  to  sleep  immediately 
afterward,  and  when  next  seen  had  had  no  return  of  pain." 
In  cases  of  neuralgia  of  the  trigeminus  dependent  on 
some  form  of  peripheral  irritation,  where  the  nerve  trunk 
in  its  passage  through  bony  canals  is  not  affected  by  dis- 
ease of  those  parts  or  by  pressure  from  tumors  in  its  vicin- 
ity, a  form  of  electrical  treatment  has  been  recommended 
by  many  which  is  not  dependent  on  influence  of  ions  intro- 
duced subcutaneously,  but  on  the  counter-irritation  effect 
of  a  weak  current  applied  to  the  painful  area.  By  this 
method  a  continuous  current  of  3  to  5  ma.  is  passed  for 
five  to  ten  minutes  with  the  anode  of  a  surface  area  of 
about  6  sqr.  cm.  applied  to  the  points  of  emergence  of  the 
branches  of  the  nerve,  the  cathode  is  attached  over  the 
upper  cervical  vertebrae  and  has  an  area  of  about  100 
sqr.  cm.  The  electrodes  must  be  firmly  applied,  care  being 
taken  to  avoid  interruptions  in  the  circuit.  The  results 
of  this  form  of  treatment  of  facial  neuralgia  is  sometimes 
very  effective  and  most  gratifying,  relief  being  obtained 
by  one  daily  treatment,  and  if  pain  recurs  the  application 
promptly  relieves  it. 


INDEX 


Abbot,  C.  H.,  on  x-rays,  185 
Abscess,  175,  275,  276,  295 
Accumulators,  62,  145 

battery,  63 

for  cautery,  102,  145 

charging,  63,  104 

for  dental  engine,  68,  103 

Edison's,  65 

for  mouth  lamps,  145 
Active  electrode,  123,  260 
Adrenalin  iron,  254 
Advantages    of   ionic    medication, 

255 
Alternating  current,  91 

transformer,  92 
Alto-frequent  current,  266 
Alveolar  abscess,  275 

process,  291 
Ammeter,  115 
Ampere,  35 
Ampere-hour,  63 
Amperemeter,  115 
Anaesthesia  of  dentine,  225,  298 

of  gums,  303 

of  pulp,  254,  301 
Anaesthetic     effect    of    high    fre- 
quency, 265 
Anion,  46 
Anode,  47 
Antrum,  176,  204 

lamp,  150 
Arrangement  of  cells,  68 


Bacteria,  effects  of  ions  on,  256 
Battery,  95 


Battery  accessories,  107 
accumulator,  102,  106 
cautery,  100 
Edison  storage,  65 
home-made,  97 
Leclanche  dry  cell,  96 

wet  cell,  100 
secondary,  62 

Bauer,  169 

Beez  scale,  168 

Benoist  scale,  168 

Bichromate  cell,  58 

Bismuth  paste,  208 

Bleaching,  electrical,  262,  303 

Boedeker,  Dr.  C.  F.,  209 

Bucky,  Dr.  G.,  184 


Calculus,  removal  of,  246 

Capacity  of  Leyden  jar,  22,  36 

Cataphoresis,  220,  225 

Cataphoric  effect,  220,  226 

Cathode,  47 

Cation,  46 

Cautery,  accumulators  for,  102 

battery,  101 

switchboards  for,  129,  148 
Cells,  31,  54 

bichromate  of  potash,  57 

Bunsen,  59 

Daniell,  60 

Grove,  60 

Leclanche  dry,  56 
wet,  54 

in  multiple  arc,  72 

in  parallel,  71 

persulphate  of  mercury,  58 

in  series,  68 


314 


INDEX 


Cells,  Smee,  57 
C.  G.  S.  system,  34 
Charging  accumulators,  63,  104 
Chemical  equivalents,  46 
Chin  electrode,  122 
Chronic  alveolar  abscess,  276 
Clark,  Mr.  C.  E.,  156,  293 
Cocaine  anaesthesia,  226 

toxic  effect  of,  218 
Coil,  induction,  82 

secondary,  84,  86 
Collectors,  109 
Colyer,  J.  F.,  246,  275 
Commutator,  88 
Condensers,  133 
Conduction,  22 

by  ions,  47,  212 
Coulomb,  35 
Creasey,  L.  C,  264 
Crypt  oradiometer,  168 
Cryptoscope,  168 
Current,  25,  28,  78,  81,  84 

alternating,  91 

collector,  107 

conducting  cord,  118 

continuous,  88 

convector,  145 

effects  on  nutrition,  233 
on  salivary  glands,  233 

from  main,  88 

heating  effects  of,  39 

interrupted,  86 

measurement  of,  33 

reverser,  118 

unit  of  strength.  35 
Cysts,  174,  196 


Daniell  cell,  60 

D'Arsonval,  40,  132 

Dead  teeth,  treatment  of,  271 

Density,  73 

Dental  electric  engine,  102 

electrical  apparatuses,  140 
Dentine  obtunding,  298 
Dieck,  167,  169,  173,  178 
Diffusion  of  current,  229 
Dissociation  of  ions,  47 
Double  collector,  111 
Dry  cell  battery,  95 


Dubois-Reymond's  coil,  87 
Dunn,  Dr.  Wm,  265 
Dynamo  currents,  88 
plan  of,  89 


E 


Edison  accumulator,  65 
Effects  of  current  on  nutrition,  233 
on  salivary  glands,  233 

of  ions  on  bacteria,  256 
Electric  diffusion,  225 

engine,  141 

furnace,  152 

gold  annealer,  155 

lathe,  143 

osmosis,  222 

syringe,  151 

sterilizer,  152 
Electrical  machine,  26 
Electricity,  galvanic,  25 

static,  28 

theories  of,  10 
Electrodes,  213 

active,  123,  260 

carbon  and  water,  121 

chin,  122 

copper,  123 

for  fistula,  124 

hand,  122 

high  frequency,  138 

indifferent,  119,  261 

Morton's,  124 

platinum,  123,  262 

pyorrhoea,  124 

root-canal,  124 

vacuum,  139 

wrist,  119 
Electrolysis,  43 

of  living  tissue,  227 
Electrolyte,  30 
Electrolytic  effects,  227 
Electro-magnet,  77 
Electro-magnetic  field,  76 

induction,  78 
Electro-motive  force,  31 
Electrons,  20 

Electro-phj'siological  effects,  211 
Electro-positive  and  negative,  50 
Electroscope,  20 
Experiments,  214,  216 


INDEX 


315 


Experiments,  cataphoric,  223 

ionic,  215,  217,  218 
Equivalents,  chemical,  46 


Farad,  35 
Faraday's  law,  46 
Faradization,  general,  233 
Film  holder,  191 

interpretation,  176 

wrapping,  182 
Finzi,  S.  N.,  216,  301 
Fluorescent  screens,  181 
Foot  warmer,  152 
Frictional  electricity,  18,  25 
Furnace,  electric,  152 


G 

Galvanic  battery,  96 

electricity,  28 
Galvano-cautery,  100 
Galvanometer,  112 
Gingival  trough,  281 
Gingivitis,  279 
Glands,  treatment  of,  264 
Gold  annealer,  155 

cyanide,  49 
Gouty  diathesis,  284 
Graphite  rheostat,  115 
Grove's  cell,  60 
Guilliminot,  48 
Gums,  anesthesia  of,  303 

hypertrophy  of,  281 


H 


Hand  electrode,  122,  261 
Heating  effects  of  current,  39 
High  frequency  apparatus,  132 

currents,  131,  264 
Holtz  machine,  25 
Hot-air  syringe,  151 

wire  ammeter,  136 
Human  body  resistance,  234 
Hydrogen  dioxide  bleaching,  307 


Immediate  extirpation  of  pulp,  302 
Incandescent  lamps,  64,  264 
Induced  currents,  78 
Induction,  19,  24,  78 

coil,  82 

battery,  88,  107 

self,  81 
Intensive  irradiation,  264 
Internal  resistance,  37 
Interrupters,  87,  162 
Ionic  medication,  212,  240,  255 
Ions,  46,  212 

adrenalin,  254 

cocaine,  254 

copper,  253 

ferrous,  214 

iodine,  253 

salicylic,  243,  255 

silver,  253 

zinc,  242,  252 
Insulators,  23 
Intensifying  serum,  178 
Iron.  30,  37 


Jack.  Dr.  Louis,  301 

Jar,  Leyden,  22,  133 

Jaws,  necrosis  of,  206,  277 

Jones,  Lewis,  on  cataphoresis,  224 

on  ionic  medication,  242 

on  ions,  212 

on  path  of  current,  288 

on  resistance,  236 
Join's  law,  39 


Kathode,  213 

Rations,  213 

Kells,  ISO 

Kirk  on  bleaching,  304 


Lambertz  stand,  170 
Lamp,  mouth,  150 


316 


JNDEX 


Lead  accumulator  plates,  62 

Leclanche  cell,  54 

Leduc  S.,  on  cocaine,  254 
on  dissociation  of  ions,  47 
on  ionic  medication,  311 

Ley  den  jar,  21,  27 

Lime,  chlorinated,  304 

Lines  of  force,  75 

Lodge,  Sir  Oliver,  20,  77 

Lupus,  142 

Lymphadenitis,  264 


M 

Magnet,  75 
Magnetic  field,  77,  80 

force,  75 
Mains,  current  from,  88 

switchboard  for,  127,  143 
Marginal  gingivitis,  279 
Measurement  of  current,  33 

of  resistance,  168,  235 

of  root  (x-ray),  190 
Milliampere-meter,  112,  136 
Monkey,  experiment  on,  216 
Morton,  J.  W.,  52,  222,  225,  239 
Motor  convector,  147 

dynamo,  91 

transformer,  131 
Motors,  140 
Mouth  lamp,  151 
Mouth  wash,  290 
Multiple  arc  connection,  72 


N 


Necrosis,  206,  208.  277 
Negative  electricity,  19 
Nerves,  motor,  230 

sensory,  231 

special,  232 
Neuralgia,  243,  308 
Nutrition,  effects  of  current  on,  233 


Ohm,  34 

Ohm's  law,  33,  38 

Optic  nerve  stimulation,  232 


i  Oral  sepsis,  281 
Orthodontia,  186 
Osmosis,  221 
Oxygen  in  bleaching,  304 
Ozone,  267 


Parallel,  cells  in,  77 

Parker,  Dr.  C.  H.,  268 

Path  of  current  in  body,  228 

Penetration  of  ions,  213 

Perforation  of  root,  275 

Peridontitis,  273 

Periodontal  disease,  280 

Persulphate  of  mercury  cell,  58 

Pfahler,  167,  207 

"Phantom"  skull,  Dieck's,  182 

Physiological  effects  of  current,  221 

Plate-holder,  .r-ray,  182 

Plates  of  accumulators,  62,  66 

Platinum  electrode,  123,  262 

Polarization,  40 

Poles,  testing  of,  42 

Potential,  29,  33 

Practical  electrical  units,  34 

Pulp  anaesthesia,  302 
septic,  271 

Pus,  periodontal,  288 

Pyorrhoea  alveolaris,  280 
diagnosis  of,  281 
treatment  of,  285,  288 


Qualimeter,  Bauer's,  168 
Quantity,  electricity,  36 
Quinine  ions,  311 


R 


Radiography,  167 
Raper,  167 
Referred  pains,  308 
Resistance,  36 

of  body,  234 

of  dead  teeth,  238 

of  dentine,  237-262 

heating  effects  of,  39,  263,  306 


INDEX 


317 


Resistance  for  heavy  currents,  128, 
140 

instruments,  128,  145 

internal  and  external,  37,  69 

of  lamps,  64 

measurement  of,  168,  235 

of  metals,  37 

Ohm's  law  of,  38,  69 

of  tubes,  168 
Resonator,  133 
Reverser,  118 
Rhein,  168 
Rheophores,  118 
Rheostats,  115 

for  direct  current.  125 
Rodent  ulcer,  242 
Rollins,  167 
Rontgen  rays,  156 
Root  sterilization,  272 


Salicylic  ions,  243,  255,  311 
Salivary  calculus,  246 

glands,  233 
Scale,  Walter,  168 

Wehnelt's,  168 
Screen,  fluorescent,  181 
Secondary  batteries,  62,  106,  145 

coil,  84 

x-rays,  184 
Self-induction,  81 
Sensitive  dentine,  298 
Sensory  nerve  effects,  231 
Septic    infection     of     periodontal 
membrane,  281 

periodontitis,  273 

pulp,  271 
Series  wound  dynamo,  90 
Shunt  wound  dynamo,  90 
Silver  ions,  253 
Smee  cell,  57 

Smith,  Hopewell,  283,  291 
Snook  rontgen  apparatus,  159,  198 
Sodium  ion,  53 
Spark-gap,  133 
Special  nerve  effects,  232 
Static  electricity,  25 

wave  currents,  264 
Statical  machine,  25 
Stereoscopic  radiography,  ISO,  188 


Sterilizers,  151 
Storage  battery,  62,  65 
Switchboards,  for  battery,  98,  100 

dental,  143 

for  ionic  medication,  127 

resistance,  125 

for  x-rays,  165 


Technique  of  dental  radiography, 
167 

of  ionic  medication,  259 
Teeth,  bleaching  of,  262,  303 

gingivitis  about  necks  of,  279 

perforation  of  roots,  275 

removal  of  calculus  from,  280 

resistance  to  current,  231,  238, 
262 

sensitive  necks  of,  286 

septic  infection,  273 

treatment  of  dead,  271 
Testing  the  poles,  42 
Therapeutic  effect  of  current,  239 

value  of  x-rays,  208 
Theories  of  electricity,  19 
Tousey,  167,  184,  191,  208,  269 
Toxic  effect  of  cocaine,  218 
Transformers,  92 

alternating  current,  129 

for  cautery,  94 

for  high  frequency,  94,  134 

motor,  131 
Tubes,  inter-oral,  281 
Turner-Dawson,  236,  243,  255 
Turner,  G.  J.,  284 


U 

Units,  practical  electrical,  34 
Uric  acid  diathesis,  284 
Use  of  x-rays,  185,  208 


Vacuum  electrodes,  13S 
Van  Woert,  168 
Volt,  35 


318 


INDEX 


Voltameter,  114 

Volta's  contact  law,  29,  51 

Voltic  cell,  31,  54 


W 

Wagner  hammer,  87 

Walter  scale,  168 

Water  electrode,  121 

Watt,  36 

Wimshurst's  machine,  26,  160 

Wire  rheostat,  117 


X-ray  diagnosis,  185 
of  abscess,  194 
of  antral  disease,  203 
of  broken  instrument,  203 
of  calculus,  197 
of  carcinoma,  207 
of  cyst,  196 
of  exostosis,  206 
of  fracture  of  jaw,  207 


X-ray  diagnosis  of  necrosis,  206 
of  pulp  stone,  201 
of  pyorrhoea,  197 
of  root  absorption,  192 
fining,  102 
fracture.  200 
length,  190 
of  sarcoma,  207 
of  tumors,  207 
of  unerupted  teeth,  186,  205 
X-rays  apparatus,  156 
and  high  frequency,  268 
dangers  to  operator,  183 
exposure,  time  of,  177 
extra  oral,  181 
tubes,  166,  168,  269 
use  of,  therapeutically,  208 


Zinc,  29,  52 
electrodes,  123 
ions,  242,  252 

Zierler,  257 


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